Astronomers have discovered a large number of black holes, both in other galaxies and in our own, and have even photographed two of them. While the black hole itself was dark, it impacted neighboring objects, either by emitting X-rays as it devoured material or by influencing an orbiting companion star. A fresh suspect, on the other hand, isn’t eating and doesn’t have a partner celebrity with whom to dance. When the gravitational force distorts space-time, light bends around it and acts as a lens. This characteristic has been exploited to improve our ability to observe distant galaxies and identify the presence of planets by causing brief brightening in more distant stars when they pass in front of us.
However, the impact was far too massive to be created by a planet when two telescopes scanning the Milky Way looking for these types of brightening occurrences (known as microlensing) picked up an example known as OB110462 in 2011. That’s one point on which opposing publications in The Astrophysical Journal agree. Casey Lam, a PhD student at the University of California, Berkeley, and her supervisor, Dr Jessica Lu, estimated the object’s mass to be between 1.6 and 4.4 times that of the Sun in a preprint published on ArXiv.org. In the other publication, a team led by Dr Kailash Sahu of the Space Telescope Science Institute analyzed the identical data to arrive at a figure of 7.1 solar masses.
The mass is too concentrated to be a gas cloud, and neither could be a planet. With so much stuff, an ordinary star would be plainly visible, leaving just two options: a neutron star or a black hole. 2.2 solar masses is estimated to be the dividing line between these two possible outcomes for big stars. If it’s more than that, it’s a black hole; if it’s less, neutron pressure prevents total collapse, resulting in a neutron star. As a result, Lam’s estimate range permits both as possibilities, but makes a black hole more plausible, whereas Salu’s number unequivocally needs a black hole (as we previously stated).
In any case, it would be the first time a dense stellar remnant without a partner star has been discovered. “We can explore and weigh these lonely, small objects using microlensing. I believe we have created a new window into these dark things that were previously unseen.” In a statement, Lu stated. Lam’s investigation uncovered four more microlensing events with masses too tiny to be black holes, two of which might be neutron stars, while massive white dwarfs are also a possibility.
Astronomers are eager to collect enough samples of single star remnants in order to assess their population in the galaxy. This will allow scientists to test predictions concerning the fraction of stars who suffer this fate. It will also allow researchers to investigate the possibility that some black holes with masses similar to these are not the result of star collapse, but rather are remnants of the Big Bang.
Every year, microlensing investigations of areas of the sky with a dense population of stars uncover roughly 2,000 microlensing occurrences. However, the majority of them involve one star crossing in front of another. It would be impossible to study all of them in the hopes of finding those created by black holes, so Lam concentrated on the ones that lasted the longest, believing that they were more likely to be caused by black holes. In a field where most occurrences endure days or weeks, OB110462 lasted two years.
The Optical Gravitational Lensing Experiment (OGLE) and Microlensing Observations on Astrophysics both discovered OB110462 (MOA). Furthermore, follow-up data from the Hubble Space Telescope indicated that the star lensed by OB110462 is still off from its proper location ten years later due to persistent gravitational distortion. Although the Hubble data has large error bars, they nonetheless give enough information to determine OB110462’s distance and mass. A third publication, which has yet to be published, builds on the findings of the previous two to propose that, while OB110462 is currently free-floating, it was formerly part of a binary pair of stars.
