Astronomers using the Gemini International Observatory have discovered the closest known black hole to Earth. It is also the first unequivocal discovery of a dormant black hole in the Milky Way. Its proximity to Earth, only 1,600 light-years away, provides an exciting target for study to advance our understanding of the evolution of binary systems. Credit: Gemini International Observatory / NOIRLab / NSF / AURA / J. da Silva / Spaceengine / M. Zamani
The Gemini North Telescope in Hawaii reveals the first dormant star cluster[{” attribute=””>black hole in our cosmic backyard.
Using the International Gemini Observatory, astronomers have discovered the closest-known black hole to Earth. This is the first unambiguous detection of a dormant stellar-mass black hole in the Milky Way. Located a mere 1600 light-years away, its close proximity to Earth offers an intriguing target of study to advance our understanding of the evolution of binary systems.
“Take the Solar System, put a black hole where the Sun is, and the Sun where the Earth is, and you get this system.” — Kareem El-Badry
Black holes are the most extreme objects in the Universe. It is believed that supermassive versions of these unimaginably dense objects reside at the centers of all large galaxies. Stellar-mass black holes — which weigh approximately five to 100 times the mass of the Sun — are much more common. In fact, there are an estimated 100 million stellar-mass black holes in the Milky Way alone. However, only a handful have been confirmed to date, and nearly all of these are ‘active’. This means that they shine brightly in X-rays as they consume material from a nearby stellar companion, unlike dormant black holes which do not.
Astronomers have now discovered the closest black hole to Earth, which the researchers have dubbed Gaia BH1. To find it, they used the Gemini North telescope in Hawai‘i, one of the twin telescopes of the International Gemini Observatory, operated by NSF’s NOIRLab.
Gaia BH1 is a dormant black hole that is about 10 times more massive than the Sun and is located about 1600 light-years away in the constellation Ophiuchus. This means it is three times closer to Earth than the previous record holder, an X-ray binary in the constellation of Monoceros. The new discovery was made possible by making exquisite observations of the motion of the black hole’s companion, a Sun-like star that orbits the black hole at about the same distance as the Earth orbits the Sun.
This animation shows a sun-like star orbiting Gaia BH1, the closest black hole to Earth, located about 1,600 light-years away. Observations of Gemini North, one of the twin telescopes of the Gemini International Observatory, operated by NSF’s NOIRLab, were crucial to constraining the orbital motion and thus the masses of the two components in the binary system, allowing the team to identify the central object as a black hole about 10 times the mass of our Sun. Credit: T. Müller (MPIA), PanSTARRS DR1 (KC Chambers et al. 2016), ESA/Gaia/DPAC
“Take the solar system, put a black hole where the sun is, and the sun is where the Earth is, and you’ll have this system,” explains Karim El-Badri, an astrophysicist at the Astrophysical Center. Harvard, Smithsonian, and Max Planck Institute for Astronomy, and lead author of the paper describing this discovery, published November 2 in Monthly Notices of the Royal Astronomical Society.
While there have been many claimed discoveries of such systems, almost all of these discoveries have subsequently been refuted. This is the first unequivocal discovery of a sun-like star in a wide orbit around a stellar-mass black hole in our galaxy.”
Although there are millions of stellar-mass black holes roaming the Milky Way, very few have been discovered through their active interactions with a companion star. As material from a nearby star rotates in the direction of the black hole, it becomes extremely hot and generates powerful X-rays and jets of material. If a black hole is not actively feeding (ie it is asleep) it simply merges with its surroundings.
“I have been searching for dormant black holes for the past four years using a wide range of data sets and methods,” Al-Badri said. “My previous attempts – as well as those of others – have given rise to an array of binary systems masquerading as black holes, but this is the first time the research has come to fruition.”
“While this potentially foreshadows future discoveries of our galaxy’s expected cluster of dormant black holes, the observations also leave a mystery to be solved — despite the shared history with its alien neighbor, why is a companion star in this binary system so normal?” – Martin Steel
The team originally identified the system as potentially hosting a black hole by analyzing data from European Space Agency Gaia spacecraft. Gaia captured the minute irregularities in the star’s motion caused by the gravity of a massive, invisible object. To explore the system in more detail, Al-Badri and his team turned to the Gemini Multi-Object Spectrograph instrument at Gemini North, which measured the companion star’s speed as it orbited the black hole and provided an accurate measurement of the period of its orbit. Gemini’s follow-up observations were crucial to constraining the orbital motion and thus the masses of the two components in the binary system, allowing the team to identify the central object as a black hole about 10 times the mass of our sun.
Al-Badri explained that “our observations of Gemini’s follow-up confirmed beyond any doubt that the binary contains an ordinary star and at least one dormant black hole.” “We were unable to find a plausible astrophysical scenario that could explain the observed orbit of a system that does not include at least one black hole.”
The team relied not only on Gemini North’s impressive monitoring capabilities but also on Gemini’s ability to provide data on a tight deadline, as the team had only a short time to make their follow-up observations.
“When we had the first indications that the system contained a black hole, we only had a week before the two objects were at their closest orbital separation. Measurements at this point are necessary to make accurate estimates of mass in a binary system,” Al-Badri said. “Gemini’s ability to provide feedback on a short time scale was critical to the success of the project. If we missed that narrow window, we had to wait another year.”
It is difficult to press hard astronomers’ current models of the evolution of binary systems to explain how the peculiar formation of Gaia BH1 arose. Specifically, the progenitor star that later turned into the newly discovered black hole was at least twenty times the mass of our sun. This means that she would only have lived a few million years. If both stars formed at the same time, that massive star would quickly turn into a supergiant, inflating and engulfing the other star before it had time to become a proper, hydrogen-burning, main sequence star like our Sun.
It’s not at all clear how a solar-mass star could survive that ring, and end up as a seemingly normal star, as observations of a binary black hole suggest. All theoretical models that allow for survival predict that the solar-mass star should have ended up in a tighter orbit than is actually observed.
This may indicate important gaps in our understanding of how black holes form and evolve in binary systems, as well as suggest the existence of an as yet unexplored group of dormant black holes in binaries.
“Interestingly, this system cannot be easily adapted by standard binary evolution models,” Al-Badri concluded. “It raises many questions about how this binary system formed, as well as how many lurking black holes there are.”
“As part of a network of space and ground-based observatories, Gemini North has not only provided strong evidence for the closest black hole to date, but also provided the first original black hole system, arranged in the usual hot gas interacting with a black hole,” said Martin Steele, Gemini Program official. for the NSF Foundation. “While this potentially foreshadows future discoveries of our galaxy’s expected cluster of dormant black holes, the observations also leave a mystery to be solved — despite the shared history with its alien neighbor, why is a companion star in this binary system so normal?”
Reference: “Sun-like star orbiting a black hole” by Karim Badri, Hans Walter Rex, Elliot Quatert, Andrew W. Howard, Howard Isaacson, Jim Fuller, Keith Hawkins, Katelyn Breivik, Kazi WK Wong, Antonio C. Rodriguez, Charlie Conroy, Glamour Shahav, Tsvi Mazeh, Frédéric Arino, Kevin B. Berdge, Dolev Bachi, Simchon Weigler, Daniel R. Weisz, Rhys Seiberger, Silvia Almada Münter and Jennifer Wuino, November 2, 2022, Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stac3140
Gemini North notes were conducted as part of the Director’s Estimated Time Program (Program ID: GN-2022B-DD-202).
Gemini International Observatory is operated by a partnership of six countries, including the United States through the National Science Foundation, Canada through the National Research Council of Canada, Chile through Agencia Nacional de Investigación y Desarrollo, Brazil through the Ministry of Science and Technology. e Inovações, Argentina through the Ministerio de Ciencia, Tecnología e Innovación, and Korea through the Korea Institute of Astronomy and Space Sciences. These participants and the University of Hawaii, which has regular access to Gemini, each maintain a “Gemini National Office” to support local users.
