Signs of black hole feeding are gone! Maybe it was a star that interrupted the feast. This event may have led to a new understanding of these mysterious objects.
At the center of a distant galaxy, a black hole is slowly consuming the disk of gas that revolves around it. When a steady trickle of gas is pulled into the massive black hole, superheated particles gather near the black hole, producing a bright X-ray light that can be seen on Earth 300 million light-years away. These superheated gas collections, known as the black hole's corona, vary significantly by up to 100 times in luminosity, brightness, or dimming as the black hole eats.
But two years ago, astronomers were surprised to discover that the X-rays from the black hole's corona in a galaxy called 1ES 1927+654 had completely disappeared, decaying 10,000-fold in about 40 days. But after that, it started to bounce almost immediately, and after about 100 days the brightness became nearly 20 times brighter than it was before the event.
X-rays from the black hole's corona are a direct byproduct of the black hole's feeding, so the disappearance of light from 1ES 1927+654 could mean that its food supply is cut off. In a new study in the Astrophysical Journal Letters, scientists speculate that an escaping star may be too close to the black hole and torn apart. If that's the case, fast-moving debris on the star could hit part of the disk and temporarily disperse the gas.
Claudio Ricci, an assistant professor at Diego Portles University in Santiago, Chile, and lead author of the study, said: "We don't usually see black holes grow like this as they grow. It was so strange that at first we thought there might be something wrong with the data. But when we see that it's real, it's very exciting. But we also don't know what we're dealing with: None of the people we've talked to have ever seen anything like this. ”
There may be a supermassive black hole at the center of almost every galaxy in the universe, like the black hole in 1ES 1927+654, with a mass millions or billions of times larger than the Sun. They grow by consuming the gases that surround them, also known as accretion disks. Because black holes don't emit or reflect light, they can't be seen directly, but light from their corona and accretion disk offers some ways to understand these dark objects.
The authors' stellar hypothesis is also supported by the fact that a few months before the X-ray signal disappeared, observatories on Earth saw disks visibly brighten in the wavelengths of visible light (wavelengths visible to the human eye). This may be due to the initial collision of star fragments with the disk.
Dig deeper
The disappearance event in 1927+654 is unique not only because of the drastic change in brightness, but also because astronomers were able to study it in depth. The visible flares prompted Ricci and his colleagues to request follow-up monitoring of the black hole using NASA's neutron star interior composition probe NICER, an X-ray telescope aboard the International Space Station. NICER observed the system a total of 265 times in 15 months. NASA's Neil Gellers Swift Observatory, which also observed the system under ultraviolet light, as well as NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) and ESA's XMM-Newton Observatory (with NASA's involvement) obtained additional X-ray monitoring
When the corona's X-rays disappeared, NICER and Swift observed low-energy X-rays from the system, so the observatories provided an uninterrupted flow of information throughout the event.
While an elusive star seems most likely to be the culprit, the authors note that there may be other explanations for this unprecedented event. A notable feature of the observations is the overall decrease in brightness but not a smooth transition: the low-energy X-rays detected by NICER every day show huge variations, sometimes 100-fold changes in brightness in just 8 hours. In extreme cases, what we know is that the black hole's corona will brighten or darken by a factor of 100, but over much longer time spans. This rapid change that occurs for months on end is extraordinary.
Erin Carla, an assistant professor of physics at the Massachusetts Institute of Technology and co-author of the new study, said: "This database has a lot of puzzles. But it's exciting because it means we're learning something new about the universe. We think the stellar hypothesis is a good topic, but I also think we're going to analyze this event for a long time. ”
This extreme variability may be more common in the cumulative disks of black holes than astronomers realize. Many of the observatories that are running and about to be established are designed to look for short-term changes in cosmic phenomena, a practice known as "time-domain astronomy" that could reveal more similar events.
Michael Lowenstein, one of the study's collaborators and an astrophysicist, worked at the NICER Mission Center at the University of Maryland Park in Greenbelt, Maryland, and NASA's Goddard Space Flight Center (GSFC). "This new study is a very good example of how the flexibility of observation scheduling enables NASA and ESA missions to study objects that evolve relatively quickly and look for long-term changes in their average behavior," he said. Will this eating black hole return to the state it was in before the outage event? Or has the system changed radically? We are continuing to observe to find out. ”
More information about this task
NICER is an astrophysical mission in NASA's Explorer Program, which leverages innovative, streamlined and efficient management methods in the field of heliophysics and astrophysical science to provide uninterrupted launch opportunities for world-class space science investigations.
On June 13, 2012, NuSTAR launched, most recently celebrating eight years of liftoff. NuSTAR is a small explorer mission led by caltech, managed by NASA's Jet Propulsion Laboratory in Southern California for the agency's Science Mission Board in Washington, D.C., in collaboration with the Technical University of Denmark and the Italian Space Agency (ASI). The spacecraft was built by Orbital Science, a company based in Dulles, Virginia. NUSTAR's Mission Operations Center is at the University of California, Berkeley, and official data is archived at NASA's Goddard Space Flight Center (GSFC) Center for The Archival Research center for high-energy astrophysical sciences. ASI provides mission ground stations and mirror data archives. Caltech manages the Jet Propulsion Laboratory for NASA.
The ESA XMM-Newton Observatory was launched from Kourou, French Guiana, in December 1999. NASA funded the components of the XMM-Newton instrument package and provided NASA with a guest observation facility at the Goddard Space Flight Center (GSFC) to support U.S. astronomers in using the observatory.
Goddard Space Flight Center (GSFC) managed the Swift mission in partnership with Penn State University in University Park, Pennsylvania, Los Alamos National Laboratory in New Mexico, and Northrop Grumman Innovation Systems in Dulles, Virginia. Other partners include the University of Leicester in the UNITED Kingdom, the Murad Space Science Laboratory at University College London in the United Kingdom, the Brera Observatory in Italy and the Italian Space Agency.
BY: Tony Greicius
FY: Glen Li
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