Triple Star System Provide Confirmation Of The Principle Of Universality Of Free Fall

A pulsar orbited by a white dwarf star, which are both orbited by another white dwarf, provide confirmation of Einstein’s Theory of Relativity. A crucial part of Albert Einstein's theory of relativity is based on a principle called the universality of free fall, which means that all falling objects accelerate identically, regardless of their mass or composition. But it was never tested before until now.

Scientists have never been able to fully test this Principle. Because showing that all objects do accelerate the same, no matter how strong the external gravitational field has some special requirements. Thanks to a unique triple star system, this key prediction of Einstein’s theory has passed one of the most rigorous tests ever.

An international team of astronomers conducted the test by combining 818 observations over six years from 3 different observatories, making approximately 27,000 measurements of a star system named PSR J0337+1715, located about 4,200 light-years from Earth. Their findings were published in the journal Nature. 

This triple star system contains three stars: A pulsar orbited closely by a white dwarf star, which is orbited by another white dwarf that is about 1 AU away, which is the same distance between Earth and the sun. Scientist investigated this Triple Star System to measure the influences of the pull of the outer white dwarf over the pull of the outer white dwarf.

Lead author Anne Archibald, a postdoctoral researcher at the University of Amsterdam, said that this is the only pulsar known to be in a system with two other stars. Triple systems are very delicate and very few survive the supernova explosion that creates the pulsar. It was the discovery of this unique system that spurred this test of Einstein’s theory. To do this test, they needed a pulsar, which has regular radio pulses with incredible density, as well as other objects in the system, Archibald explained. “The pulsar — a rapidly rotating neutron star — rotates 366 times per second, and beams of radio waves produce pulses at regular intervals and we can use these pulses to track the pulsar. If the pulsar and the inner white dwarf fall differently towards the outer white dwarf, then the pulses would arrive at a different time than expected.




Archibald and her colleagues used three kinds of observations to make very delicate measurements.  They were measuring if the pulsar moved the same way as the inner white dwarf or not. They made frequent observations taken with the Westerbork Synthesis Radio Telescope in the Netherlands. The less frequent but long (10-hour) observations were made with the Robert C. Byrd Telescope at Green Bank, West Virginia and short monthly observations with the very sensitive William E. Gordon Telescope at Arecibo, Puerto Rico. Having all these three telescopes allowed them to cross-check them against each other Which was very essential to confirm that test was giving correct results.

During their observation they ran into many changes, for example, every March line of sight to the pulsar passes within 2.1 degrees of the sun. The solar wind at that point introduces delays in the radio signals they observe. Unfortunately, the solar wind flows out in different directions and different amounts on different days, so compensating for these delays was difficult.

The Pulsar was observed with radio telescope but the observations of inner white dwarf were made with the optical telescope. By there optical observation they measured the motion of the inner companion’s orbit by measuring the Doppler shifts of the white dwarf’s spectrum.

Archibald said, they did not detect any difference between the accelerations of the neutron star and inner white dwarf, and if there is a difference, it would be no more than three parts in a million.

They couldn't drop the stars off a tower, but as the two inner objects move around their orbit with the outer companion, they are continually falling toward it. If the pulsar experienced a different acceleration from the white dwarf, its orbit would be shifted in a way they could detect.

In Einstein's theory, gravity itself has mass, so an object with really strong gravity could behave differently, In fact, once you have an object with strong gravity, Einstein's theory is almost the only one where objects with strong gravity fall the same way as normal objects. So, this is why we needed to use a pulsar

Astronomy is a wonderful way to find out what's out there in the universe, but this sort of observation is the only way to improve our understanding of a force as fundamental as gravity.

If You Have Any Queries Then Feel Free To Ask Us Down In The Comment Section And Visit To The Science Thinkers Again. As Always Stay Curious And Thank You  

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The Van Allen Belts | Its Effect On Astronauts

There is an invisible magnetic force field surrounding our planet, protecting us from harmful solar winds that could annihilate Earth. But, this protective blanket is also a swirling ring full of deadly radiation and to leave Earth's atmosphere astronauts have to pass through it.

The Van Allen belts are rings of energetically charged particles that have been captured by Earth's magnetic field. They got their name from the Physicist named James Van Allen. Back in the 1950s, Van Allen launched a rockoon, a rocket lifted by a balloon above the atmosphere and it detected the first hint of radiation at higher altitudes. Then Explorer 1, the first American satellite to orbit Earth, launched on January 13, 1958, confirmed that Earth's magnetosphere was trapping the subatomic particles.

The Van Allen belts were the first major scientific discovery of early Space Age and they posed a serious challenge for space travel. High-speed subatomic particles can tear through DNA, increasing the risk of cancer and other desires. So sending astronauts through these particles is not ideal and even though they are flying in a shielded spacecraft, doses of radiation can still seep through. But there is no way around the Van Allen belts. In order to reach space, astronauts have to fly through them.

There are Two belts, First the inner belt which is comprised of protons and then the outer belt which has mostly high energy-electrons. One solution, proposed by Mr Van Allen himself, suggested detonating a nuclear boom in the inner belt to clear out some of the subatomic particles. Van Allen's plan never executed, but in 1962, the United States did carry out a nuclear test in space, dubbed StarFish Prime. They wanted to see if detonating a 1.4 megaton boom in low-Earth orbit could augment and expand the Van Allen Belts, but the explosion actually ends up adding more radiation around our planet.

So, for the Apollo mission, NASA  had to create a radiation barrier within the spacecraft and figure out a trajectory that avoided the thickest, most radioactive parts of the belts while travelling as fast as possible. Scientists determined that if the speed of the Apollo spacecraft was about 25,000 kilometres per hour, it would take a spacecraft about 52.8 minutes to pass through the belts. Based on that information scientists found that the radiation doses received during that amount of time would be, at most, 11.4 rads and that's without the protection of a spacecraft. Since a lethal radiation dosage for a human is 300 rads in one hour, so NASA deemed the missions a go. After all that, it turned out that during the Apollo missions the average radiation doses on the skin of the astronauts came out to be 0.38 rad which is about the same radiation you would receive by getting two CT scans of your head.

So while the Van Allen belts are lethal, they could really only kill an astronaut if they were to spend several days in their radioactive vicinity and despite the challenges the belts create when leaving Earth, we should actually be thanking them for protecting life on our planet from utter annihilation.

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