EVEN STAR SYSTEMS HAVE IDENTITY CRISES

A double star system has been flipping between two alter egos, according to observations with Chandra X-ray Observatory and The Karl G. Jansky Very Large Array(VLA). Using nearly a decade and a half worth of Chandra data, researchers noticed that a stellar duo behaved like one type of object before switching its identity and then returning to its original state after a few years. This is a rare example of a star system changing its behaviour in this way.

Astronomers found this volatile double, or binary, system in a dense collection of stars, the globular cluster Terzan 5, which is located about 20,000 light-years from Earth in the Milky Way galaxy. This stellar duo, known as Terzan 5 CX1, has a neutron star in close orbit around a star similar to the Sun, but with less mass.

In this new image of Terzan 5 (right), low, medium and high-energy X-rays detected by Chandra are coloured red, green and blue respectively. On the left, an image from the Hubble Space Telescope shows the same field of view in optical light. Terzan 5 CX1 is labelled as CX1 in the Chandra image.

In binary systems like Terzan 5 CX1, the heavier neutron star pulls material from the lower-mass companion into a surrounding disk. Astronomers can detect these so-called accretion disks by their bright X-ray light, and refer to these objects as low-mass X-ray binaries.

Spinning material in the disk falls onto the surface of the neutron star, increasing its rotation rate. The neutron star can spin faster and faster until the roughly 10-mile-wide sphere, packed with more mass than the Sun, is rotating hundreds of times per second. Eventually, the transfer of matter slows down and the remaining material is swept away by the whirling magnetic field of the neutron star, which becomes a millisecond pulsar. Astronomers detect pulses of radio waves from these millisecond pulsars as the neutron star's beam of radio emission sweeps over the Earth during each rotation.

While scientists expect the complete evolution of a low-mass X-ray binary into a millisecond pulsar should happen over several billion years, there is a period of time when the system can switch rapidly between these two states. Chandra observations of Terzan 5 CX1 show that it was acting like a low-mass X-ray binary in 2003, because it was brighter in X-rays than any of the dozens of other sources in the globular cluster. This was a sign that the neutron star was likely accumulating matter.

In Chandra data taken from 2009 to 2014, Terzan 5 CX1 had become about ten times fainter in X-rays. Astronomers also detected it as a radio source with the VLA in 2012 and 2014. The amount of radio and X-ray emission and the corresponding spectra agree with expectations for a millisecond pulsar. Although the radio data used did not allow a search for millisecond pulses, these results imply that Terzan 5 CX1 underwent a transformation into behaving like a millisecond pulsar and was blowing material outwards. By the time Chandra had observed Terzan 5 CX1 again in 2016, it had become brighter in X-rays and changed back to acting like a low-mass X-ray binary again.

To confirm this pattern of “Jekyll and Hyde” behaviour, astronomers need to detect radio pulses while Terzan 5 CX1 is faint in X-rays. More radio and X-ray observations are planned to search for this behaviour, along with sensitive searches for pulses in existing data. Only three confirmed examples of these identity-changing systems are known, with the first discovered in 2013 using Chandra and several other X-ray and radio telescopes.

Two other recent studies have used Chandra observations of Terzan 5 to study how neutron stars in two different low-mass X-ray binaries recover after having had large amounts of material dumped on their surface by a companion star. Such studies are important for understanding the structure of a neutron star’s outer layer, known as its crust.

In one of these studies, of the low-mass X-ray binary Swift J174805.3–244637 (T5 X-3 for short), material dumped onto the neutron star during an X-ray outburst detected by Chandra in 2012 heated up the star's crust. The crust of the neutron star then cooled down, taking about a hundred days to fall back to the temperature seen before the outburst. The rate of cooling agrees with a computer model for such a process.

In a separate Chandra study of a different low-mass X-ray binary in Terzan 5, IGR J17480–2446 (T5 X-2 for short) the neutron star was still cooling when its temperature was taken five and a half years after it was known to have an outburst. These results show this neutron star’s crust ability to transfer, or conduct, heat may be lower than what astronomers have found in other cooling neutron stars in low-mass X-ray binaries. This difference in the ability to conduct heat may be related to T5 X-2 having a higher magnetic field compared to other cooling neutron stars, or being much younger than T5 X-3.

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A DARK COSMIC WEB THAT TIES THE UNIVERSE TOGETHER

After counting all the normal, luminous matter in the obvious places of the universe (galaxies, clusters of galaxies and the intergalactic medium) about half of it is still missing. So not only is 85% of the matter in the universe made up of an unknown, invisible substance dubbed dark matter, we can't even find all the small amount of normal matter that should be there.

This is known as the "missing baryons" problem. Baryons are particles that emit or absorb light, like protons, neutrons or electrons, which make up the matter we see around us. The baryons unaccounted for are thought to be hidden in filamentary structures permeating the entire universe, also known as "the cosmic web".

The universe is permeated by a vast, invisible web, its tendrils weaving through space. But despite organizing the matter we see in space, this dark web is invisible. That's because it is made up of dark matter, which exerts a gravitational pull but emits no light. 

That is, the web was invisible until now. For the first time, researchers have illuminated some of the darkest corners of the universe. Now a new study, published in arXiv, offers a better view that will enable us to help map what it looks like.

A long time ago, the universe was hotter, smaller and denser than it is now. There wasn't much variation in density from place to place. space was much more cramped overall and no matter where you went, things were pretty much the same.

But there were tiny, random differences in density. Those nuggets had slightly more gravitational pull than their surrounding neighbourhood, so matter tended to flow into them and made them bigger. 

In this way,  they developed an even stronger gravitational influence which helped them pull more matter in and so on and so on for billions of years. Simultaneously, as the nuggets grew, the spaces between them emptied out. Eventually, the dense patches grew to become the first stars, galaxies and clusters, while the spaces between them became the great cosmic voids. 

The vast majority of matter in our universe is dark; it does not interact with light or with any of the normal matter. As a result, much of the cosmic web is completely invisible to us.

Now we can easily spot the great cosmic voids because there are no galaxies to illuminate these spaces as we know there is no matter there. It’s just truly empty space. But the grandeur of the cosmic web lies in the delicate lines of the filaments themselves. Stretching for millions of light-years, these thin tendrils of galaxies act like great cosmic freeways crossing black voids, connecting bright urban clusters.

Those filaments in the cosmic web are the hardest part of the web to study. They have some galaxies but not a lot. And they have all sorts of lengths and orientations; in comparison, the clusters and voids are geometric child's play. So, even though we've known of the existence of filaments, through computer simulations, for decades, we have had a hard time actually, you know, seeing them.

Recently, a team of astronomers made a major advancement in mapping our cosmic web, publishing their results at the arXiv database. First, they took a catalogue of luminous red galaxies (LRGs) from the Baryon Oscillation Spectroscopic Survey (BOSS) survey. LRGs are massive beasts of galaxies, and they tend to sit in the centres of dense blobs of dark matter. And if the LRGs sit in the densest regions, then lines connecting them should be made of the more delicate filaments.

But staring at the space between two LRGs isn't going to be productive; there isn't a lot of stuff there. So, the team took thousands of pairs of LRGs, realigned them and stacked them on top of each other to make a composite image.

Using this stacked image, the scientists counted all the galaxies that they could see, adding up their total light contribution. This allowed researchers to measure how much normal matter made up the filaments between the LRGs. Next, the researchers looked at the galaxies behind the filaments, and specifically, at their shapes.

As light from those background galaxies pierced the intervening filaments, the gravity from the dark matter in those filaments gently nudged the light, ever so slightly shifting the images of those galaxies. By measuring the shear (the amount of shifting), the team was able to estimate the amount of dark matter in the filaments.

That measure lined up with theoretical predictions (another point for the existence of dark matter). The scientists also confirmed that the filaments weren't entirely dark. For every 351 suns' worth of mass in the filaments, there was 1 suns' worth of light output.

It's a crude map of the filaments, but it's the first, and it definitely shows that while our cosmic web is mostly dark, it's not completely black. This will help reveal more mystery surrounding the cosmic web and provide us with a definitive census of the matter in the universe.

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LEARN ABOUT THE SECOND BRIGHTEST OBJECT IN THE CONSTELLATION ORION: BETELGEUSE

Betelgeuse is a red supergiant star roughly 700 light-years away from our own Solar System. Betelgeuse is usually the eleventh-brightest star in the night sky. After Rigel, the second brightest object in the constellation Orion, the rust-coloured star has attracted attention from astronomers for its relative closeness and potential for collapsing in a spectacular supernova event within the next 100,000 years.

While we all would love nothing better than to see a visible star go boom, the chances anybody living today will experience such a spectacle are slim. Very slim.

Estimates on its remaining lifetime depend largely on accurate measurements of its mass and rotation, which thanks to the scarcity of nearby companions to help judge its gravitational pull, have proven hard to pin down. Guesses of the star's mass vary from 10 to 20 solar masses, with a size most likely around 11 to 12 times the mass of our own Sun.

Fortunately, Betelgeuse also happens to be big enough and close enough for astronomers to make out some details of its structure. This material is spread out over a vast distance in a blob that's only roughly spherical in shape. If Betelgeuse was at the centre of our Solar System, its body would stretch out to brush the edges of Jupiter's orbit. 

Being a mere 700 light-years away, the star's end in a supernova explosion would be easily visible to the average sky-watcher with the naked eye. Its usual visual magnitude (a measure of how bright something appears to us) varies from a relatively bright 0 to a slightly dimmer 1.3. For comparison, the highly reflective planet Venus is a touch below -4, with the Moon having an average of just under -13 apparent magnitude).

For unknown reasons, at the end of 2019 and the start of 2020, the brightness of the red supergiant dipped further than usual, to around 1.5. Should Betelgeuse collapse and go supernova, the released energy would see its brightness rival the Moon's, all concentrated in a star-like point. Yet to be seen.

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STUDY OF MUONS PARTICLE COULD CHANGE SCIENCE AS WE KNOW IT

You may never have heard of muons before, but these particles are crucial to our understanding of the universe. In a milestone study published in the journal Nature, researchers announced that they have overcome one of the biggest challenges to studying these fundamental particles. The study heralds a new era of research into the properties and structure of matter and that includes us, humans.

Muons are fundamental particles and are very similar to electrons, but 207 times heavier. That means they carry much more energy than electrons. They are crucial to our understanding of our physical world, because they provide information about the properties and structure of matter.

But studying muons is difficult. Fundamental particles like muons (think the neutrino) are only visible at high energies and for microseconds. Physicists have to use particle colliders and accelerators to glimpse their properties. These instruments slam particle beams together at a very high speed and capture data from the resulting explosions, allowing researchers to peek into the subatomic world. This is exactly what physicists have been doing at the Large Hadron Collider, which infamously smashed proton beams together in order to discover and study the theorized Higgs boson, another elusive fundamental particle.

We'd known about muons for many years, but we never managed to put them into a particle accelerator before. Now, after decades of research, Rogers and a team of hundreds of international scientists have outlined how to get closer to creating a first-of-its-kind particle collider that can blast beams of muons at much higher energies than any existing colliders. The invention has the potential to reveal exotic particles that exist only in theory or even entirely new particles scientists had never thought of before.

When you smash beams of particles together, what happens is you make all sorts of exotic new particles, like force carriers or like novel forms of matter, And by looking at all the different sorts of particles which can be created, we can try and understand things about how matter gets stuck together. How matter sticks together is at the basis of our understanding of how everything in the universe is made, because everything is made of matter.

This result is a fundamental landscape change. It doesn’t happen very often. It’s like a Lego piece, to build our future plans. A piece of lego that you can multiply and play with and use to build new things. We can move forward in previously unexplored ways, But a new piece of lego can change how we are going to arrange it.

Despite their obvious importance, colliders like the famous Large Hadron Collider, are massive instruments that cost huge amounts of money and are very hard to build and manage. So far, there is no particle collider designed for muons, which means there is no way of studying and understanding them (even though muons were among the first particles to be ever discovered, in 1936).

For many years the biggest hurdle for studying muons was that we never managed to put them into a particle accelerator. Well, The researchers cracked the problem of “ionization cooling of muons” — basically cooling the smashing beams of particles so they’re easier for current instruments to capture and analyze, rather than having the muons flying all over the place uncontrollably.

The researchers had to develop a technique which can take this messy beam and turn it into a really nice laser-like beam: cooling the beam. So if you imagine the beam is like a hot gas, it's flying along really fast. What we want to do is reduce the temperature of that gas. The temperature of the muons at production is roughly 10 billion degrees Celsius. We're trying to go from this diffused gas to something which is more like a laser beam. Cooling techniques have been discovered before, but they usually take minutes or hours to do. What they had developed is a radically different sort of cooling, which can take effect on timescales of billions of a second.

The muon collider itself would be similar in scale to either the Tevatron, which was a machine which was built at Fermilab near Chicago, or the Large Hadron Collider. You're looking at a machine which is several kilometres in length, with these extremely strong magnets, and the cost scale is similar to those machines.

Muons themselves are interesting beasts and there are applications which we will really only just starting to understand if we start building beyond accelerators. Muons' properties hint at these future applications. For example, muons are much more penetrating than X-rays, which means they can be used to look inside things that are too thick for x-rays to image. This includes pyramids and volcanoes, for example.

Muons may provide a completely new way to reach further into the energy frontier of particle accelerators that simply cannot be achieved at the present time, and we might not have a way to get there otherwise. But while the study represents a milestone along the road to developing the first-ever muon colliders, don't hold your breath too soon. There are many more years of research ahead for Rogers’ team to turn this into a reality, he says. But when we do get there, what we find may be truly unimaginable.

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WHAT IS NASA'S ARTEMIS PROGRAM?

Through the Artemis lunar exploration program. NASA is committed to landing astronauts, including the first woman and the next man, on the Moon by 2024. NASA will use innovative new technologies and systems to explore more of the Moon than ever before. NASA will collaborate with commercial and international Space Agency to establish sustainable missions for various research and deep understanding of the Universe.

Artemis program will be helpful to demonstrate new technologies, capabilities humans have achieved in the past decades and it will also help us to test new innovative technologies. Through the Artemis program, humans will have a permanent presence on the Moon As we have on Space because of the International Space Station. Most of all It will Inspire a new generation and encourage careers in Space exploration. 

NASA’s powerful new rocket, the Space Launch System (SLS), will send astronauts aboard the Orion spacecraft nearly a quarter-million miles from Earth to lunar orbit. Astronauts will dock Orion at the Gateway and transfer to a human landing system for expeditions to the surface of the Moon. They will return to the orbital outpost to board Orion again before returning safely to Earth.

Before sending humans, Nasa will send a suite of science instruments and technology demonstrations to the lunar surface through commercial Moon deliveries beginning in 2021. After that NASA will fly two missions around the Moon to test its deep space exploration systems. NASA is working toward launching Artemis I, an uncrewed flight to test the SLS and Orion spacecraft together, followed by the Artemis II mission, the first SLS and Orion test flight with a crew. NASA will land astronauts on the Moon by 2024 on the Artemis III mission and about once a year thereafter. 

What We Are Going To Achieve With  Artemis Program?

• Find and use water and other critical resources needed for long-term exploration
• Investigate the Moon’s mysteries and learn more about our home planet and the universe.
• Learn how to live and operate on the surface of another celestial body where astronauts are just three days from home.
• Prove the technologies we need before sending astronauts on missions to Mars, which can take up to three years roundtrip.

At the end Mars is the main goal, but before Mars Astronaut will explore the entire surface of the Moon with human and robotic explorers. Going forward to the Moon will be the next step of our generation, the generation ready for space travel.

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10 SCIENTIFIC INSTRUMENTS ON BOARD THE SOLAR ORBITER TO TRANSFORM OUR UNDERSTANDING OF THE SUN

NASA-ESA Solar Orbiter is set to launch into space on Sunday, February, 9, 2020 at 11:03 p.m Eastern. And it packs ten powerful scientific instruments on board that will shed unprecedented light on our Sun. The mission is an ambitious collaboration between the European Space Agency and NASA. It aims to resolve some of the biggest mysteries surrounding the Sun.

Scientists have observed the Sun since the dawn of astronomy, but still don't have the answers to questions like how the Sun’s magnetic field operates, how it affects the star’s polar regions or what drives the solar wind. One key question scientists hope to answer with the mission is what drives solar cycles “moments that occur every 11 years when the Sun's magnetic poles switch”.

We know that the Sun exhibits this 11-year activity cycle. We don’t really know what drives this cycle of 11 years and we can’t predict how strong the next cycle is going to be. To get those answers, the Solar Orbiter will travel closer to the Sun than any other spacecraft before it, essentially flying outside the confines of the Solar System in order to peer down at the Sun, studying the star from a high altitude.

The spacecraft carries 10 scientific instruments. Six of the instruments are remote sensing, capturing images of the Sun, while the remaining four are in-situ instruments. which will measure solar wind, plasma and other aspects of the environment around the spacecraft.

The unique feature of this mission is that these instruments are able to work together, because they are able to talk to each other. If one of the instruments detects an interesting observation, then it will notify other relevant instruments so that they can do their own measurements, too. There work as a team is totally awesome. 

THE INSTRUMENTS ARE:

• EUI: Extreme Ultraviolet Imager
• Metis
• PHI: Polarimetric and Helioseismic Imager
• SoloHi: Solar Orbiter Heliospheric Imager
• SPICE: Spectral Imaging of the Coronal Environment
• STIX: X-ray Spectrometer/Telescope
• EPD: Energy Particle Detector
• MAG: Magnetometer
• RPW: Radio and Plasma Waves
• SWA: Solar Wind Plasma Analyzer

EUI: EXTREME ULTRAVIOLET IMAGER

This instrument will capture ultra-violet images of the lower layers of the solar atmosphere, which lie just above the surface of the Sun. The imager will help scientists understand how the Sun’s lower atmosphere heats up, and how that influences the larger corona or the outermost part of the solar atmosphere. The imager is located in an optics box behind the spacecraft’s heat shield.

METIS

Metis will capture images of the Sun’s outer atmosphere. The instrument will image the corona, which is dimmer than the rest of the atmospheric layers, in both visible and extreme ultraviolet light. It manages this feat by blocking light from Sun’s bright surface. Metis will capture the corona at a distance of approximately 302,000 and 908,000 miles from the Sun’s surface, closer than any other coronagraph has gotten to the Sun. By observing this area of the Sun’s atmosphere, scientists can gain a better understanding of how the Sun affects the rest of the heliosphere.

PHI: POLARIMETRIC AND HELIOSEISMIC IMAGER

PHI is made up of two telescopes — a full-disk telescope, which views the whole Sun at any given time, and a high-resolution telescope, which views just a portion of the Sun, revealing its fine structure in detail. The two telescopes produce magnetograms, which are maps of the magnetic peaks and valleys on the Sun’s surface. Together they enable scientists to estimate the magnetic field in the solar corona and heliosphere. The Sun’s magnetic field is key to understanding its behaviour. It is believed to be the main driving force behind the 11-year solar cycle whereby the Sun’s North and South poles flip.

SOLOHI: SOLAR ORBITER HELIOSPHERIC IMAGER

SoloHi is a visible-light telescope that will image sunlight as it is reflected off electrons in the solar wind. The telescope will focus on the interplanetary medium or the space that lies between the Sun and the planets. This area is crucial to predicting when and understanding how eruptions from the Sun will take place and whether or not they will affect Earth. At its closest approach, the telescope will capture a region from about 2.25 million miles to approximately 18 million miles from the Sun.

SPICE: SPECTRAL IMAGING OF THE CORONAL ENVIRONMENT

SPICE is an extreme ultraviolet spectrometer designed to map the plasma or streams of hot gas, that erupt from the Sun’s surface in the form of the solar wind. The instrument will collect data on the density and flow of the solar material.

STIX: X-RAY SPECTROMETER/TELESCOPE

This instrument is designed to survey X-rays as they erupt from the surface of the Sun during solar flares. STIX will take note of the timing, location and intensity of each X-ray burst from the Sun. Doing so will help scientists figure out how these solar flares erupt. The instrument has a wide-field view, meaning it can see the entire Sun at any given time. Solar flares pose a threat to space equipment such as satellites and they are a hazard for astronauts journeying through deep space.

EPD: ENERGETIC PARTICLE DETECTOR

EPD measures electrons and other particles emitted by the Sun, as well as their timing and distribution. It will help scientists understand how solar radiation forms by breaking down components of the solar wind plasma and the Sun’s magnetic field.

MAG: Magnetometer

This instrument will measure the strength and direction of the magnetic field around the Solar Orbiter. The Magnetometer will help scientists trace the origins of the magnetic field and solar wind plasma in the corona. It will also reveal how energetic-particle radiation travels out into the Solar System following solar eruptions.

SWA: Solar Wind Analyzer Suite

As the Sun blows solar wind towards the spacecraft, this instrument will measure more than 99% of all the charged particles emitted by the star. The measurements can help scientists in determining exactly what the solar wind is made up of and where the streams of solar wind come from.

RPW: Radio and Plasma Waves

This instrument is designed to measure changes in the electric and magnetic fields around the spacecraft. The data will help identify the role plasma plays in the solar wind, whether it helps in its acceleration or heating.

The data which will be collected from the craft's 10 scientific instruments will help scientists resolve some mysteries regarding our host star, namely what drives solar wind and how it affects the Solar System, including our own planet Earth.

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What Is A Neutron Star?

Neutron stars are created when giant stars die in supernovae and their cores collapse, with the protons and electrons essentially melting into each other to form neutrons. Neutron stars are city-size stellar objects with a mass about 1.4 times that of the sun. Born from the explosive death of another, larger stars, these tiny objects pack quite a punch.

When stars three times as massive as the sun explodes in a violent supernova, their outer layers can blow off in an often-spectacular display, leaving behind a small, dense core that continues to collapse. Gravity presses the material in on itself so tightly that protons and electrons combine to make neutrons, yielding the name "neutron star." This is how it is named neutron star.

Ordinary stars maintain their spherical shape because they have the gravity of their gigantic mass tries to pull their gas toward a central point, but it is balanced by the energy from nuclear fusion in their cores, which exerts an outward pressure. At the end of their lives, when stars are burned through their available fuel, their internal fusion reactions cease. The stars' outer layers rapidly collapse inward, bouncing off the thick core and then blasting out again as a violent supernova.

After the star went supernova the dense core continues to collapse, generating pressures so high that protons and electrons are squeezed together into neutrons, as well as lightweight particles called neutrinos that escape into the distant universe. The end result is a star whose mass is 90% neutrons, which can't be squeezed any tighter, and therefore the neutron star can't break down any further.

Neutron stars pack their mass inside a 20-kilometre (12.4 miles) diameter. They are so dense that a single teaspoon would weigh a billion tons — assuming you somehow managed to snag a sample without being captured by the body's strong gravitational pull. On average, gravity on a neutron star is 2 billion times stronger than gravity on Earth. In fact, it's strong enough to significantly bend radiation from the star in a process known as gravitational lensing, allowing astronomers to see some of the backsides of the star.

The power from the supernova that birthed it gives the star an extremely quick rotation, causing it to spin several times in a second. Neutron stars can spin as fast as 43,000 times per minute, gradually slowing over time.

The properties of neutron stars are utterly out of this world — a single teaspoon of neutron-star material would weigh a billion tons. If you were to somehow stand on their surface without dying, you'd experience a force of gravity 2 billion times stronger than what you feel on Earth.

An ordinary neutron star's magnetic field might be trillions of times stronger than Earth's. But some neutron stars have even more extreme magnetic fields, a thousand or more times the average neutron star. This creates an object known as a magnetar.  

Starquakes on the surface of a magnetar — the equivalent of crustal movements on Earth that generate earthquakes — can release tremendous amounts of energy. In one-tenth of a second, a magnetar might produce more energy than the sun has emitted in the last 100,000 years.

Astronomers first theorized about the existence of these bizarre stellar entities in the 1930s, shortly after the neutron was discovered. But it wasn't until 1967 that scientists had good evidence for neutron stars in reality. A graduate student named Jocelyn Bell at the University of Cambridge in England noticed strange pulses in her radio telescope, arriving so regularly that at first, she thought they might be a signal from an alien civilization, according to the American Physical Society. The patterns turned out not to be E.T. but rather radiation emitted by rapidly spinning neutron stars.

If a neutron star is part of a binary system that survived the deadly blast from its supernova (or if it captured a passing companion), things can get even more interesting. If the second star is less massive than the sun, it pulls mass from its companion into a Roche lobe, a balloon-like cloud of material that orbits the neutron star. Companion stars up to 10 times the sun's mass create similar mass transfers that are more unstable and don't last as long.

Stars more than 10 times as massive as the sun transfer material in the form of a stellar wind. The material flows along the magnetic poles of the neutron star, creating X-ray pulsations as it is heated.

By 2010, approximately 1,800 pulsars had been identified through radio detection, with another 70 found by gamma-rays. Some pulsars even have planets orbiting them — and some may turn into planets.

Types of neutron stars

Radio pulsars

Recycled pulsars

Millisecond pulsars

Magnetar

Soft gamma-ray repeater

Anomalous X-ray pulsar

Low-mass X-ray binaries (LMXB)

Intermediate-mass X-ray binaries (IMXB)

High-mass X-ray binaries (HMXB)

Accretion powered pulsar

Pulsars

Some neutron stars have jets of materials streaming out of them at nearly the speed of light. As these beams pan past Earth, they flash like the bulb of a lighthouse. Scientists called them pulsars after their pulsing appearance. Normal pulsars spin between 0.1 and 60 times per second, while millisecond pulsars can result in as much as 700 times per second.

When X-ray pulsars capture the material flowing from more massive companions, that material interacts with the magnetic field to produce high-powered beams that can be seen in the radio, optical, X-ray or gamma-ray spectrum. Because their main power source comes from the material from their companion, they are often called "accretion-powered pulsars." "Spin-powered pulsars" are driven by the star’s rotation, as high-energy electrons interact with the pulsar's magnetic field above their poles. Young neutron stars before they cool can also produce pulses of X-rays when some parts are hotter than others.

As material within a pulsar accelerates within the magnetosphere of a pulsar, the neutron star produces gamma-ray emission. The transfer of energy in these gamma-ray pulsars slows the spin of the star.

The supernova that gives rise to a neutron star imparts a great deal of energy to the compact object, causing it to rotate on its axis between 0.1 and 60 times per second, and up to 700 times per second. The formidable magnetic fields of these entities produce high-powered columns of radiation, which can sweep past the Earth-like lighthouse beams, creating what's known as a pulsar.

The flickering of pulsars is so predictable that researchers are considering using them for spaceflight navigation.

"Some of these millisecond pulsars are extremely regular, clock-like regular," Keith Gendreau of NASA's Goddard Space Flight Center in Maryland, told members of the press in 2018.

"We use these pulsars the same way we use the atomic clocks in a GPS navigation system," Gendreau said.

Magnetars

The average neutron star boasts a powerful magnetic field. Earth's magnetic field is around 1 gauss, and the sun's magnetic field is around a few hundred gauss, according to astrophysicist Paul Sutter. But a neutron star has a trillion-gauss magnetic field.

Magnetars have magnetic fields a thousand times stronger than the average neutron star. The resulting drag causes the star to take longer to rotate. 

"That puts magnetars in the No. 1 spot, reigning champions in the universal 'strongest magnetic field' competition," Sutter said. "The numbers are there, but it's hard to wrap our brains around them."

These fields wreak havoc on their local environments, with atoms stretching into pencil-thin rods near magnetars. The dense stars can also drive bursts of high-intensity radiation.

Get too close to one (say, within 1,000 kilometres, or about 600 miles), and the magnetic fields are strong enough to upset not just your bioelectricity (rendering your nerve impulses hilariously useless) but your very molecular structure. In a magnetar's field, you just kind of dissolve."

Collision Of Neutron Star

Like normal stars, two neutron stars can orbit one another. If they are close enough, they can even spiral inwards to their doom in an intense phenomenon known as a "kilonova."

The collision of two neutron stars made waves heard 'round the world in 2017 when researchers detected gravitational waves and light coming from the same cosmic smashup. The research also provided the first solid evidence that neutron-star collisions are the source of much of the universe's gold, platinum and other heavy elements.

"The origin of the really heaviest chemical elements in the universe has baffled the scientific community for quite a long time," Hans-Thomas Janka, a senior scientist at MPA, said in a statement. "Now, we have the first observational proof for neutron star mergers as sources; in fact, they could well be the main source of the r-process elements," which are elements heavier than iron, like gold and platinum.

The powerful collision released enormous amounts of light and created gravitational waves that rippled through the universe. But what happened to the two objects after their smashup remains a mystery.

"We don't actually know what happened to the objects at the end," David Shoemaker, a senior research scientist at MIT and a spokesman for the LIGO Scientific Collaboration, said at a 2017 news conference. "We don't know whether it's a black hole, a neutron star or something else." The observations are thought to be the first of many to come.

"We expect that more neutron-star mergers will soon be observed and that the observational data from these events will reveal more about the internal structure of matter," study lead author Andreas Bauswein, from the Heidelberg Institute for Theoretical Studies in Germany, said in a statement.

Can Neutron Star Become Blackhole?

When a star dies, it spent all of its energy and then collapses. Their difference lies in their parent star. When a dying star has a mass which is 1.4 to 3 times that of the sun, it will form a neutron star. Stars with a mass greater than 3 times the sun's mass, a black hole is formed. The maximum mass of a neutron star is 3 solar masses. If it gets more massive than that, then it will collapse into a quark star, and then into a black hole.

Some Interesting  Fact

1. In just the first few seconds after a star begins its transformation into a neutron star, the energy leaving in neutrinos is equal to the total amount of light emitted by all of the stars in the observable universe.

2. It’s been speculated that if there were life on neutron stars, it would be two-dimensional.

3. The fastest known spinning neutron star rotates about 700 times each second.

4. The wrong kind of neutron star could wreak havoc on Earth.

5. Despite the extremes of neutron stars, researchers still have ways to study them.

Researchers have considered using the stable, clock-like pulses of neutron stars to aid in spacecraft navigation, much like GPS beams help guide people on Earth. An experiment on the International Space Station called Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) was able to use the signal from pulsars to calculate the ISS’s location to within 10 miles (16 km). 

But a great deal remains to be understood about neutron stars. For instance, in 2019, astronomers spotted the most massive neutron star ever seen — with about 2.14 times the mass of our sun packed into a sphere most likely around 12.4 miles (20 km) across. At this size, the object is just at the limit where it should have collapsed into a black hole, so researchers are examining it closely to better understand the odd physics potentially at work holding it up. 

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Accretion Of A Giant Planet Onto A White Dwarf Star

The Neptune-sized planet, which orbits an Earth-sized star, is being slowly evaporated by the white dwarf, causing the planet to lose some 260 million tons of material every day.

For the first time, astronomers have discovered evidence for a giant planet orbiting a tiny, dead white dwarf star. And, surprisingly, the Neptune-sized planet is more than four times the diameter of the Earth-sized star it orbits.

"This star has a planet that we can't see directly. But because the star is so hot, it is evaporating the planet, and we detect the atmosphere it is losing. In fact, the searing star is sending a stream of vaporized material away from the planet at a rate of some 260 million tons per day." Boris Gänsicke from the University of Warwick said in a press release.

The new discovery serves as the first evidence of a gargantuan planet surviving a star's transition to a white dwarf. It suggests that evaporating planets around dead stars may be somewhat common throughout the universe. And because our Sun, like most stars, will also eventually evolve into a white dwarf, the finding could even shed light on the fate of our solar system.

The white dwarf in question, dubbed WDJ0914+1914, sits about 1,500 light-years away in the constellation Cancer. Although the white dwarf is no longer undergoing nuclear fusion like a normal star, its lingering heat means it's still a blistering 49,500 degrees Fahrenheit (25,000 Celsius). That’s some five times hotter than the Sun.

Researchers initially flagged the smouldering stellar core for follow-up after sifting through about 7,000 white dwarfs identified by the Sloan Digital Sky Survey. When the team analyzed the unique spectra of WDJ0914+1914, they detected the chemical fingerprints of hydrogen, which is somewhat unusual. But they also picked out signs of oxygen and sulfur — elements they had never seen in a white dwarf before.

In order to get a better grasp of what was happening in the strange system, the team of researchers used the X-shooter instrument on the ESO's Very Large Telescope in Chile to carry out follow-up observations. Based on the more detailed look, the researchers learned that the unusual elements they thought were embedded in the white dwarf were actually coming from a disk of gas churning around the dead star.

"At first, we thought that this was a binary star with an accretion disk formed from mass flowing between the two stars. However, our observations show that it is a single white dwarf with a disk around it roughly 10 times the size of our Sun, made solely of hydrogen, oxygen and sulfur. Such a system has never been seen before, and it was immediately clear to me that this was a unique star." said Gänsicke.

After realizing just how unusual the white dwarf really was, the team shifted their focus to figuring out what the heck could create such a system.

"It took a few weeks of very hard thinking to figure out that the only way to make such a disk is the evaporation of a giant planet," said Matthias Schreiber, an astronomer at the University of Valparaiso in Chile, who was vital to determining the past and future evolution of the bizarre system. Their detailed analysis of the disk's composition matched what astronomers would expect if the guts of an ice giant like Uranus and Neptune were vaporized into space.

Based on Schreiber's calculations, the white dwarf's extreme temperature means it's bombarding the nearby giant planet — which is located 0.07 astronomical unit (AU) from the star, where 1 AU is the Earth-Sun distance — with high-energy photons. This is causing the planet to lose its mass at a rate of more than 3,000 tons per second.

But according to the paper, published Wednesday in Nature, "As the white dwarf continues to cool, the mass-loss rate will gradually decrease, and become undetectable in about 350 million years. And by then, the paper adds, the giant planet only will have lost "an insignificant fraction of its total mass," or about 0.04 Neptune masses.

Because the giant planet is located so close to the white dwarf, the researchers say it should have been destroyed during the stars' red giant phase. That is unless it migrated inward after the star transitioned to a white dwarf. 

"This discovery is major progress because over the past two decades we had growing evidence that planetary systems survive into the white dwarf stage," said Gänsicke. "We've seen a lot of asteroids, comets, and other small planetary objects hitting white dwarfs, and explaining these events requires larger, planet-mass bodies farther out. Having evidence for an actual planet that itself was scattered in is an important step."

The ultimate fate of our solar system. In 5 billion years, when the Sun burns through the last of the hydrogen in its core, it will move on to fusing concentric shells of hydrogen around its now-inert core. This unstable process will cause the Sun to balloon into a red giant, meaning it will swallow Mercury, Venus, and likely Earth.

But as the Sun expands, its gravitational grasp on its outer envelope of material gets more and more tenuous. Eventually, it will shed its outer layers into space. And once it does that, an alien astronomer would see a beautiful planetary nebula surrounding the Sun's burnt-out, incredibly hot core — known as a white dwarf.

In a companion paper also published Wednesday in Astrophysical Journal Letters, Schreiber and Gänsicke explore this scenario, detailing how the future white-dwarf Sun should, like WDJ0914+1914, evaporate our solar system's giant planets.

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What If We had Two Suns in The Solar System?

For a long time, this was a purely theoretical question. Over the past decade or so, however, astronomers have found more than a dozen confirmed instances of “circumbinary planets”—that is, planets that orbit around a close double star.

A particularly interesting case is the planet Kepler-1647b, which circles two roughly sunlike stars. This planet also resides in the “habitable zone,” the region around the two stars where the planet could have the right temperature for liquid water.

What if Earth had two suns instead of one? Let’s consider a simple scenario. Suppose we replaced the sun with two closely matched stars, each half as bright as the Sun. In that case, the amount of energy reaching the Earth would still be the same, and life would still be possible here. Such equal-mass binaries are not uncommon, so this scenario seems perfectly plausible.

The mass of each of our new suns would be about 85% of the mass of our current sun. That may seem surprising, but the luminosity of a star is extremely sensitive to mass. Roughly speaking, luminosity goes as the 4th power of mass, so doubling the mass of a star increases its brightness by a factor of 16. A 15% mass reduction is enough to cut a star’s brightness in half.

The combined mass of Sun 1 and Sun 2 would be 1.7 times the mass of our current sun. Since their total gravity would be stronger, the length of a year would be a bit less: about 280 days instead of 365 days. Not that radical of a change, really.

So far so good. But would the Earth be stable in its new configuration, orbiting around two stars instead of one? The case of Kepler-1647b and other circumbinary stars gives a strong YES answer here. As long as the distance to the planet is at least about 4 times as great as the separation between the two stars, the planet just happily orbits around the stars’ centre of mass. If Sun 1 and Sun 2 are less than 15 million kilometres apart, then all of the planets in the solar system (even Mercury) could potentially be stable.

Just to be safe, let’s put the stars closer together, about 5 million kilometres apart. That’s not so different than the two stars of Kepler-1647, which are about 7 million miles apart. Our Sun 1 and Sun 2 would orbit each other once every 10 days or so. They would also each rotate with a 10-day period, which would make them a little more active than our current sun, but not outrageously so. The Kepler-1647 stars are reasonably peaceful.

The two suns would probably appear to orbit each other roughly edge-on as seen from Earth, which would lead to a strange new phenomenon: an eclipse of the sun by another sun! Because of the 10-day orbit, Sun 1 and Sun 2 would pass in front of each other every 5 days. The eclipses would last about 6 hours, and at peak would reduce the amount of energy reaching the Earth by about 30%–40%, depending on the exact geometry.

Eclipse days would be chilly, but the periods of reduced sunshine would be brief enough to average out smoothly into Earth’s overall climate. The double suns wouldn’t even look all that strange in the sky. At maximum separation, Sun 1 and Sun 2 would be only 2 degrees apart in the sky, just enough to give shadows a double edge. For about a half-day on either side of an eclipse, they'd seem to merge, though if they slipped behind a cloud you'd see an odd, oval shape from the overlapping disks. Sunsets would be pretty, a little different each night.

All the evidence so far, then, is that a planet like Tatooine in Star Wars really could exist, and Earth would do just fine if it were orbiting a double star instead of our one lonely sun. There’s really just one huge unsettled question: Could such a planet form in the first place?

Kepler-1647b is a giant gas planet, nearly twice the mass of Jupiter. Even the smallest known circumbinary planet, called Kepler-453b, is a heavyweight, bigger than Neptune.

It may be that the environment around a double star is too chaotic to create small, rocky planets like Earth. Then again, it’s also possible that other Earths with two suns are common, and our telescopes simply are not sensitive enough to find them. At least, not yet.

Fortunately, better instruments are coming soon. In the coming decade, the PLATO space telescope and huge new ground-based observatories like the Giant Magellan Telescope and the Extremely Large Telescope will tell us a lot more about all kinds of planets around other stars—including possible Earthlike planets with double suns lighting up their skies.

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