Record breaker! Newly found black hole is closest to Earth known
The black hole record books have just been rewritten.
A black hole lurking about 10 times more massive than our sun just 1,560 light-years from Earth, a new study reports. That’s about twice as close as the previous proximity champion.
The newly discovered object, a stellar-mass black hole called Gaia BH1, is in a binary system whose other member is a sun-like star. That star is about as far from its companion black hole as Earth is the sunwhich makes Gaia BH1 very special indeed.
“While there are many purported detections of these kinds of systems, almost all of these discoveries have subsequently been disproved,” study lead author Kareem El-Badry, of the Harvard-Smithsonian Center for Astrophysics in Massachusetts and the Max Planck Institute for Astronomy in Germany. said in a statement (opens in new tab). “This is the first unequivocal detection of a Sun-like star in broad orbit around a stellar black hole in our galaxy.”
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Astronomers think our galaxy is home to about 100 million stellar black holes, light-eating objects five to 100 times more massive than the Sun.
However, their small size makes these bodies relatively difficult to detect, especially with a telescope. (Gravitational Wave Detectors have had more success recently, finding evidence of mergers involving these objects.) And the ones scientists see are usually “X-ray binaries,” black holes that pull material from a companion star into an accretion disk. This rapidly spinning dust and gas emits X-rays, high-energy light that some powerful telescopes can see.
However, not all stellar black holes that live in binary systems are actively feeding. Finding these sleeping objects is even more difficult and requires different strategies.
The researchers used such an alternative technique in the new study. They delved into data collected by the European Space Agency (ESA) Gaia spacecraftthat accurately maps the positions, velocities and orbits of about 2 billion stars in the Milky Way.
One of those stars is Gaia’s companion BH1. Its movement shows small irregularities – an indication that something massive and unseen is pulling on it due to gravity.
The Gaia measurements suggested a black hole could be that trigger, but the scientists needed more data to be sure. So they studied the star with a number of ground-based instruments, including the Gemini North and Keck 1 telescopes in Hawaii and the Magellan Clay and MPG/ESO telescopes in Chile.
These follow-up observations, combined with the Gaia data, allowed the team to get a closer look at the system’s measure. The invisible object contains the mass of 10 suns, they determined, and orbits the system’s center of mass about once every 186 Earth days. And it must be a black hole.
“Our follow-up observations of Gemini confirmed beyond a reasonable doubt that the binary star contains a normal star and at least one sleeping black hole,” El-Badry said. “We could not find a plausible astrophysical scenario that could explain the observed orbit of the system that does not involve at least one black hole.”
For example, if the invisible object in Gaia BH1 were a star, it would be much brighter than its companion and therefore easier to see. But none of the team’s observations revealed a hint of a second star in the system.
The Gaia BH1 system is intriguing, and not just because it’s relatively close to us. (In the cosmic scheme of things, anyway; the Milky Way’s famous spiral disk is about 100,000 light-years wide.) The research team isn’t sure how the star and black hole got to their current position.
The mass of Gaia BH1 indicates that the star that died and formed must have been huge — at least 20 solar masses or so. Such giants only live for a few million years, and they blow up enormously before giving up the ghost.
Modeling work suggests that such a puff would likely have destroyed the companion before it had a chance to evolve into a Sun-like star (if the two were born at the same time). Or, if it survived, it should have landed in a much tighter orbit than the one it currently occupies, the researchers said.
“Interestingly, this system cannot be easily accommodated in standard binary evolution models,” El-Badry said. “It raises a lot of questions about how this binary system formed and how many of these dormant black holes exist.”
The new study (opens in new tab) was published online today (Nov. 4) in the journal Monthly Notices of the Royal Astronomical Society.
Mike Wall is the author of “Outside (opens in new tab)(Grand Central Publishing, 2018; illustrated by Karl Tate), a book on the search for extraterrestrial life. Follow him on Twitter @michaeldwall (opens in new tab). follow us on twitter @Spacedotcom (opens in new tab) or on facebook (opens in new tab).
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