Is evidence of a twin Earth buried in unexamined Kepler Mission data? Kepler’s last observing campaign, Campaign 19, started on August 29, 2018 after the spacecraft’s configuration had been modified in 2014 in order to adapt to a change in thruster performance, and NASA officially changed the mission’s name from Kepler to K2 while using the same telescope. During the following 27 days, Kepler observed more than 30,000 stars in the constellation of Aquarius. The stars included dozens of known and suspected exoplanet systems — including the well-known TRAPPIST-1 system with its seven Earth-sized planets.
A Fascinating Discovery
NASA woke up the Kepler spacecraft and maneuvered it into a stable configuration on October 10 that allowed the mission team to download the latest data with the least amount of fuel consumption. Earlier 2018, astronomers stumbled upon a fascinating finding: thousands of black holes likely exist near the center of our galaxy. The X-ray images that enabled this discovery weren’t from some state-of-the-art new telescope. Nor were they even recently taken – some of the data was collected nearly 20 years ago by NASA’s Chandra X-Ray Observatory. The researchers discovered the black holes by digging through old, long-archived data.
What Else Lies Hidden, Buried in the Data?
Astronomers have long looked for up to 20,000 black holes that previous research predicted should be concentrated around the Milky Way’s core. Sagittarius A* is surrounded by a halo of gas and dust that provides the perfect breeding ground for massive stars, which can then give rise to black holes after they die, said Chuck Hailey, co-director of the astrophysics lab at Columbia University. In addition, the powerful gravitational pull of Sagittarius A* can pull in black holes from outside this halo, he added.
“The Milky Way is really the only galaxy we have where we can study how supermassive black holes interact with little ones because we simply can’t see their interactions in other galaxies,” Hailey said in a statement. “In a sense, this is the only laboratory we have to study this phenomenon.”
The Density Cusp
However, until now, researchers failed to detect such a heavy concentration of black holes, called a “density cusp.” “There are only about five dozen known black holes in the entire galaxy — 100,000 light-years wide — and there are supposed to be 10,000 to 20,000 of these things in a region just six light-years wide that no one has been able to find,” Hailey said in the statement. “There hasn’t been much credible evidence.”
“There has been no new data concerning the density cusp in the Galactic Center, Chuck Hailey told The Daily Galaxy. “Further elucidation of this issue must await more sensitive and higher angular resolution X-ray telescopes, such as will fly on the future Lynx mission in several decades. Or we simply wait until we see an X-ray outburst (these happen every few years) from one of the large population of silent black holes in the Galactic Center. Either way, patience is required.
Black Hole Cluster Detected
“However,” he adds, “recent observations by Eduardo Vitral and Gary A. Mamon of the Institut d’Astrophysique de Paris, using Hubble Space Telescope and Gaia, suggest a cluster of black holes residing in the core collapse globular cluster NGC 6397, one of the two nearest globular clusters to Earth contains about 400,000 stars. While the environments of the Galactic Center and the core of a globular cluster are quite different, this is a very hopeful step on the way to discovering more black hole concentrations around our Galaxy.”
“Our study is the first finding to provide both the mass and the extent of what appears to be a collection of mostly black holes in a core-collapsed globular cluster,” said Vitral.
“Our analysis would not have been possible without having both the Hubble data to constrain the inner regions of the cluster and the Gaia data to constrain the orbital shapes of the outer stars, which in turn indirectly constrain the velocities of foreground and background stars in the inner regions,” added Mamon, attesting to an exemplary international collaboration.
Vitral and Mamon also noted that this discovery raises the question of whether mergers of these tightly packed black holes in core-collapsed globular clusters may be an important source of gravitational waves recently detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) experiment.
The at the top of the page provides a view of Sagittarius A*, the supermassive black hole at the center of the Milky Way, taken with the Chandra X-ray Observatory (circled in green). The black hole is visible as a bright spot because it is emitting some of its occasional X-ray flares. Surrounding it are other X-ray sources caused by binary systems with smaller black holes. (Nature and Hailey, et. al.)