Note4Students

From UPSC perspective, the following things are important :

Prelims level: Speed of light, Neutron stars, various terms mentioned

Mains level: Not Much

light

Scientists have spotted something that appeared to be moving 7 times faster than the Speed of Light in a supernova like event.

What is the news?

In 2017, astrophysicists observed an unusual feat among the stars.
The Laser Interferometer Gravitational-Wave (LIGO) observatories recorded a signal which indicated that two massive and dense stellar bodies had merged to form a third body, likely a black hole.
An unusual jet of matter was observed that gave an illusion of travelling faster than light.

Can matter move faster than Light?

From the data, it appeared the jets of matter were moving seven times faster than light.
The researchers explain the reason behind the discrepancy is due to something called superluminal motion.
Since the jet of matter reaches Earth at the speed of light, the light it emits at later points has a relatively shorter distance, making it appear faster than it actually is.
After more calculations, astronomers found the real speed to be at least 99.7 percent of the speed of light (3 × 10^8 m / s).

The data of same incident has been recorded by the Global Astrometric Interferometer for Astrophysics (GAIA) spacecraft and Hubble (James Web) Space Telescope
Using it, scientists confirmed that the above picture is correct.

Scientists have also measured more accurately a factor called the Lorenz factor which scales with the actual speed of the particles in the jet.
Unlike earlier estimates which placed this factor at about 4, the present paper estimates this factor to be over 40.
This is because they measure the speed of the relativistic jet to be close to 9997c, where “c” is the speed of light.

Source is clearly as massive neutron stars merging to give a black hole and throwing off relativistic jets of particles in the process.

Neutron stars are stellar corpses, left behind after a star has undergone a supernova explosion and reached the end of its lifetime.
They are extremely dense, containing more mass than the sun in a sphere that is a few tens of kilometre wide.
The observation of particles moving at seven times the speed of light is an illusion.
This happens in cases where a source moves (towards us) with a velocity that is very close to light’s velocity.
This has been seen in many active galactic nuclei — galaxy centres that harbour black holes — and binary star systems within our galaxy, where one of the stars is a black hole.
Mostly, black holes are responsible for producing such fast-moving material.

Normally, if one were making these measurements from earth-based telescopes, it would require data from radio telescopes spaced apart by intercontinental distances.
This technique is called Very Long Baseline Interferometry (VLBI) and was used in the earlier papers.

The significance of the paper is that now, we have learnt that neutron star mergers can result in material moving with speeds as high as 0.9997c.
Earlier results using Very Long Baseline Interferometry had pegged this value at about 0.938c.
And with the new results this lower limit has been improved.
Even earlier, with VLBI, it was understood that it was a neutron-star merger that produced such ultra-relativistic material.