International Space Agencies – Missions and Discoveries

The illusion of being faster than light: how a star problem was solved


From UPSC perspective, the following things are important :

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

Mains level : Not Much


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).

Crossing the speed of light: An illusion

  • 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.

How to assess it?

  • 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.

How are they observed?

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

Merging neutron stars: Faking to cross speed of light

  • 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.

How is this illusion created?

  • 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.

Significance of this study

  • 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.


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