A sun-like star contributes to the discovery of the closest black hole to planet Earth
Since the 1980s, scientists have been studying supermassive black holes. which resides at the center of most of the giant galaxies in the universe. And in April 2019, the Event Horizon Telescope team released the first-ever image of a supermassive black hole.
Karl Schwarzfeld developed his theory that established the existence of black holes in 1916, after finding a solution to field equations from Einstein's general theory of relativity.
After that, astronomers succeeded in observing black holes for the first time in the middle of the twentieth century, using indirect methods, which is observing the effects of black holes on the objects surrounding them and on space.
These observations provided an opportunity to test the laws of physics under extreme conditions, and to provide new knowledge about the forces that shaped the universe.
In a recent study, an international team of researchers relied on available data from the Gaia Observatory to detect a sun-like star with an unusual orbit. The team concluded that because of the nature of the star's orbit, it must be part of a binary system with a black hole. Thus, this black hole is the closest to our solar system, and indicates the presence of quite a few inactive black holes in our galaxy.
Research team leader Karim El Badry is a member of the Harvard Astronomy Society in collaboration with the Harvard-Smithsonian Center for Astronomy and the Max Planck Institute for Astronomy. He was joined by researchers from Caltech and Berkeley, the Flatirion Institute for Astronomy, the Weizmann Institute of Science, the Paris Observatory, MIT's Calvi Institute for Astronomy and Space Research, and several other universities. The paper on their findings will be published in the monthly publication of the Royal Astronomical Society.
Al-Badri indicated in a media message that this research is part of an expanded campaign to identify dormant black holes that mate with ordinary stars within the Milky Way.
“I have been searching for dormant black holes for four years, using large databases and various methods,” he says. My previous attempts have turned up a multitude of black hole-like binaries, but this time the search seems to have finally paid off.”
For their study, El-Badri and colleagues relied on data from the European Space Agency's Gaia Observatory. This decade-long mission has measured the positions, distances, and motions of nearly a billion astronomical objects, such as stars, planets, galaxies, comets, and asteroids.
The Gaia mission aspires to build the most accurate 3D guide to the universe by tracking the motion of objects as they orbit the center of the Milky Way galaxy. This method is known as astrometry.
El-Badry and colleagues examined 168,065 stars from the Gaia data release III, which are likely to be two bodies orbiting together.
Their analysis of the data found a possible candidate - a yellow star named DR3 4373465352415301632 - according to the Gaia data. For convenience, the team named it Gaia BH1. Al-Badri and his colleagues determined that this star shares an orbit with a black hole. Based on the data of their observation of the orbit of the star.
“We focused on spectral analysis of the star using several other telescopes, to make sure that Gaia's research method is correct,” El-Badri says. And to exclude any other possibilities, there are no logical explanations left except that this mass is indeed a dark black hole.
To confirm their observations, the team analyzed radial velocity measurements of Gaia BH1 with several independent telescopes and spectrometers, including HIRES, MPG/ESO, X-Shooter, GMOS, and LAMOS.
The team relied on the same means used to find exoplanets, namely Doppler spectral analysis, and those observatories provided spectrum analysis that enabled the team to measure the gravitational forces affecting the orbit. These observations and measurements confirmed that the orbit of Gaia BH1 contains a hidden companion 10 times the mass of the Sun.
Al-Badri indicated that this discovery may establish the existence of the first black hole in the Milky Way that was not detected by X-ray emissions or any other energy images.
Al-Badri stated: “The models predict that the Milky Way contains approximately 100 million black holes, of which we discovered only 20. All that has been detected before has been observed with X-ray binaries: the black hole engulfing the companion star makes it shine so brightly in the X-ray range, due to the conversion of matter's gravitational potential energy into light.
All of this is only the tip of the iceberg, as many large objects hidden in binaries that are very far from each other may appear to us. Our discovery of Gaia BH1 sheds light on this type of object.”
This discovery, if scientists confirm its validity, means that the Milky Way galaxy is full of idle black holes. They are defined as black holes that are not inferred from the bright ring around them or from the radiation flux, or ultrafast jets emanating from its poles, as in the case of quasars.
The influence of these objects on the evolution of stars and planets would be very profound in our galaxy if they were indeed widespread in it. But it is also possible that this inert black hole is a unique case rather than an indication of the proliferation of counterparts in the galaxy.
Al-Badri and his team are waiting for the fourth edition of Gaia's data until their hypothesis is confirmed, and although the date of its publication is not yet known, it will contain all the information that was collected over a period of five years, which is the duration of that hypothetical mission.
The edition will include a directory of the latest astronomical, photometric and radial velocity measurements of all observable stars, black holes, binaries, galaxies and exoplanets.
It is worth noting that the fifth and final version will contain data from the original and additional mission as well; That is, over 10 years.
“The next release of Gaia is likely to enable the discovery of dozens of similar systems, based on the frequency of occurrence of those binaries identified by Gaia BH1,” El-Badry says.
It is difficult to know the number of homologues based on just one object. It could be just a stroke of luck, or an outlier. We are very excited to conduct studies of the distributions of these objects, which the many samples will make available to us.”
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