Scientists have mapped the environment around a stellar black hole that is 10 times the mass of the Sun, using the payload of NASA's Inside Composite Nucleus (NICER) aboard the International Space Station.
NICER detected newly discovered black hole X-ray light called MAXI J1820 + 070 (J1820), as it consumed material from a companion star. X-ray waves formed "light echoes" that reflected the swirling gas near the black hole and revealed changes in the size and shape of the environment.
"NICER allowed us to measure light echoes closer to a stellar mass black hole than before," said Erin Kara, University of Maryland astrophysicist, College Park and NASA's Goddard Space Flight Center in Greenbelt, Md., Who presented the study . discoveries at the 233rd meeting of the American Astronomical Society in Seattle. "Previously, these inner accretion disk light echoes were only seen in supermassive black holes, which are millions to billions of solar masses and undergo slow changes. Stellar black holes like the J1820 have much smaller masses and evolve much faster changes happen on human time scales ".
An article describing the findings, led by Kara, appeared in the Jan. 10 issue of Nature and is available online.
J1820 is located about 10,000 light-years away towards the constellation of Leo. The companion star of the system was identified in a survey conducted by the European Space Agency's Gaia mission, which allowed researchers to estimate its distance. Astronomers did not know of the presence of the black hole until March 11, 2018, when an explosion was detected by the All-sky X-ray Image Monitor (MAXI) of Japan's Aerospace Exploration Agency, also aboard the space station. The J1820 has gone from a totally unknown black hole to one of the brightest sources in the X-ray sky for a few days. NICER moved quickly to capture this dramatic transition and continues to follow the tail of the eruption.
"NICER was designed to be sensitive enough to study weak and incredibly dense objects called neutron stars," said Zaven Arzoumanian, NICER's chief science officer at Goddard and co-author of the article. "We are pleased with how useful it is also proven in the study of these black holes with stellar X-ray mass."
A black hole can suck gas from a nearby companion star into a ring of material called the accretion disk. Gravitational and magnetic forces heat the disk to millions of degrees, making it hot enough to produce X-rays on the inner parts of the disk, near the black hole. Explosions occur when instability in the disk causes a flood of gas to move inward toward the black hole, like an avalanche. The causes of disk instabilities are poorly understood.
Above the disk is the crown, a region of subatomic particles around 1 billion degrees Celsius (1.8 billion degrees Fahrenheit) that shines on high-energy X-rays. Many mysteries remain about the origin and evolution of the crown. Some theories suggest that the structure could represent an early form of the high-velocity particle jets that these types of systems generally emit.
Astrophysicists want to better understand how the inner edge of the accretion disk and the crown above it change in size and shape as a black hole adds material from its companion star. If they can understand how and why these changes occur in stellar mass black holes over a period of weeks, scientists could clarify how supermassive black holes evolve over millions of years and how they affect the galaxies in which they reside.
One method used to map these changes is called X-ray reverberation mapping, which uses X-ray reflections in the same way that sonar uses sound waves to map underwater terrain. Some X-rays of the corona travel directly to us, while others light the disc and reflect back into different energies and angles.
The mapping of X-ray reverberation of supermassive black holes showed that the inner edge of the accretion disk is very close to the event horizon, the point of no return. The crown is also compact, getting closer to the black hole than to much of the accretion disk. Previous observations of X-ray echoes of stellar black holes, however, have suggested that the inner edge of the accretion disk could be very distant, up to hundreds of times the size of the event horizon. The stellar mass J1820, however, behaved more like its supermassive cousins.
While examining NICER's J1820 observations, Kara's team saw a decrease in the delay, or delay, between the initial flash of X-rays coming directly from the crown and the echo of the disk flare, indicating that X-rays traveled shorter and shorter distances before being reflected. From 10,000 light-years away, they estimated that the crown contracted vertically from about 100 to 10 miles – it's like seeing something the size of a blueberry shrink to something the size of a poppy seed in the distance from Pluto.
"This is the first time we've seen this kind of evidence that the crown is dwindling during this particular phase of the explosion," said co-author Jack Steiner, an astrophysicist at the Kavli Institute of Astrophysics and Space at the Massachusetts Institute of Technology. Research in Cambridge. "The crown is still quite mysterious, and we still have a weak understanding of what it is. But now we have evidence that the thing that is evolving in the system is the structure of the crown itself."
To confirm the decrease in the delay time was due to a change in the crown and not the disk, the researchers used a signal called the iron K line, created when the corona X-rays collide with iron atoms in the disk, causing fluorescence. Time runs more slowly in stronger gravitational fields and at higher speeds, as stated in Einstein's theory of relativity. When the iron atoms closest to the black hole are bombarded by the light from the core of the crown, the X-ray wavelengths emitted are stretched because the time is moving more slowly to them than to the observer (in this case, NICER ).
Kara's team discovered that the elongated K line of J1820 remained constant, which means that the inner edge of the disk remained near the black hole – similar to a supermassive black hole. If the shortest delay time were caused by the inner edge of the disk moving further inward, then the iron line K would have stretched further.
These observations provide scientists with new insights into how the material tapers into the black hole and how energy is released in that process.
"The J1820 NICER observations have taught us something new about stellar mass black holes and how we can use them as analogues to study supermassive black holes and their effects on galaxy formation," said co-author Philip Uttley, an astrophysicist of the University. of Amsterdam. "We've seen four similar events in NICER's first year, and it's remarkable. It looks like we're on the verge of a breakthrough in X-ray astronomy."
NICER is an Astrophysical Opportunity Mission within the NASA Explorer program, which offers frequent flight opportunities for world-class scientific research from space using innovative, streamlined and efficient management approaches in the fields of heliophysics and astrophysics. The NASA Space Technology Mission Directory supports the SEXTANT component of the mission, demonstrating pulsed spacecraft navigation.
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