JUL 28, 2018 5:37 AM PDT

Star Ran Away From Black Hole, Leaving a Part of Its Light Behind

WRITTEN BY: Daniel Duan

An artistic rendition of the star S2 escaping from the  black hole Sagittarius A* (ESO)

In a recent news conference, scientists from the European Southern Observatory (ESO) announced that their Very Large Telescope (VLT) in Chile witnessed a change of a star's light spectrum as it zipped past a massive black hole: the gravitational pull was so strong, the starlight became stretched, exactly matching Einstein's prediction on the motion of a star travelling through extreme gravity.

What the astronomers observed is a common physical phenomenon known as the redshift. A closely related term you might have heard of is the Doppler effect: whenever you hear a vehicle or a plane traveling from near to far, the pitch of the sound they make gets lower because of the wavelength of the sound wave increases.

The same principle applies to electromagnetic radiation such as the visible light. As the wavelength of a light signal creeps close to the long (or "red") end of the spectrum, a redshift happens.

For astronomy enthusiasts, a familiar example would be a cosmological redshift: due to the expansion of the universe, the distant starlight, usually million light years away from Earth, shows redshift.

At the heart of the Milky Way, sits a supermassive black hole called Sagittarius A*. Because it emits no light, it took astrophysicists a lot of efforts to identify. By observing nearby stars orbit around it and occasional destruction of flyby objects, astronomer confirmed its existence.

With a mass 4 million times that of the sun, it sinks deep into the space-time fabric and its superduper gravitational field whips every object in its vicinity to very high speed.

In May 2018, the ESO astronomers witnessed three stars passing very close to Sagittarius A*. S2, the fastest one among the three, had its speed clocked at 15.5 million miles per hour or 25 million kilometers per hour. It is approximately 2.5% of light speed or over 30 times faster than our sun orbiting the center of Milky Way.

On top of that, using two advanced instruments that are parts of the VLT,  GRAVITY (a device for precision narrow-angle astrometric measurement and interferometric imaging) and SINFONI (Spectrograph for INtegral Field Observations in the Near Infrared), scientists noticed the difference in the spectroscopic profile S2, which showed a warped light signature. This is consistent with predictions based on Einstein's general relativity.

In Einstein's theory of general relativity, the energy and momentum of matter dictate the curvature of the spacetime. That's why in the powerful gravitational field of Sagittarius A*, a part of the radiation emitted by S2 got inevitably pulled in, resulting in a loss of energy to the black hole and elongated wavelength.  

For more than two decades, the ESO researchers have been pointing their VLT telescope at the center of the Milky Way, in the hope of finding the true proof of general relativity. No wonder the observation was hailed as "the climax of a 26-year-long observation campaign".

Artist's impression of the star S2 passing close to  supermassive black hole (ESO)

Source: Space.com/ESO

About the Author
Master's (MA/MS/Other)
Graduated with a bachelor degree in Pharmaceutical Science and a master degree in neuropharmacology, Daniel is a radiopharmaceutical and radiobiology expert based in Ottawa, Canada. With years of experience in biomedical R&D, Daniel is very into writing. He is constantly fascinated by what's happening in the world of science. He hopes to capture the public's interest and promote scientific literacy with his trending news articles. The recurring topics in his Chemistry & Physics trending news section include alternative energy, material science, theoretical physics, medical imaging, and green chemistry.
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