This Astrophysicist Is Hunting for a Binary Black Hole at the Center of Our Galaxy

Monday, 16 December 2019 - 3:57PM
Astrophysics
Black Holes
Monday, 16 December 2019 - 3:57PM
This Astrophysicist Is Hunting for a Binary Black Hole at the Center of Our Galaxy
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Credit: NAOJ
Every galaxy has a supermassive black hole at its center. But a new theoretical abstract asks us to consider whether binary black holes at the center of a galaxy might not only be possible, but common – and goes on to declare that there could be a second black hole hidden in the Milky Way.


Sagittarius A* is a supermassive black hole located 24,000 light-years away at the center of our Milky Way galaxy. It has a mass of 4 million Suns. Sagittarius A* is surrounded by a tight ring of stars, and it's these stars that scientists first measured to determine the existence of Sagittarius A*.


Smadar Naoz, an astrophysicist and an associate professor of physics and astronomy at the University of California in Los Angeles, led a team of scientists in studying the sheaves of data we have from star S0-2, which resides in this ring of stars. S0-2 orbits the black hole Sagittarius A* and makes a close approach every 16 years. By studying this star's behavior, we can determine how Sagittarius A* is acting on it and make inferences about what this black hole is doing.


But what about its friend? Based on what Naoz and her team have deduced, if there is a companion black hole to Sagittarius A* it must be no more than 100,000 times our Sun's mass in order for star S0-2 to orbit as it does.


So, how do you hunt down a second black hole where one already exists? The team proposes that expanding their research from one star to many stars will enable them to calculate enough orbits and compare them against the averages to determine whether a second, smaller black hole might be gravitationally acting on these stars. Studying the light these stars emit as they approach and retreat from the black hole(s) will also give astrophysicists more information thanks to Einstein's theory of gravitational redshift, where gravity expands or compresses the wavelengths of visible light. If there's a second black hole, scientists will see unexpected changes in these colors.


The team also wants to study the accretion (or debris) around Sagittarius A* – if there is a second black hole, it almost certainly would have impacted how the first one formed. Lastly, the team plans to capitalize on the planned LISA mission to measure gravitational waves, which are "ripples in space-time" caused by neutron stars and black holes.


LISA is a European Space Agency (ESA) mission with contributions from NASA. It will launch three separate spacecraft spaced millions of miles apart to measure gravitational waves. The mission is slated for the early 2030s.


A paper has been published on Cornell University's ArXiv, an online repository of scholarly papers that have not yet been peer-reviewed.
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