Black holes are immensely strong gravitational wells of spacetime that even light can never escape. Across Milky Way, tens of millions of them are pulling in gas and dust from an orbiting star resulting in spectacular bursts of X-ray light that bounce and echo the gas to illuminate their extreme surroundings.
Science Daily reported that astronomers from MIT analyzed the echoes coming from the nearby black hole X-ray binaries to reconstruct a black hole's immediate, extreme vicinity, which will tell how they evolve during an outburst. The researchers used a new automated search tool called "Reverberation Machine" to detect the echoes to understand how the outbursts affect galaxies.
Eight New Echoing Black Hole Binaries Discovered In Milky Way Galaxy: Listen to the Eerie Sounds They Make
Using X-ray Echoes to Map Black Hole's Vicinity
Scientists study black holes because they are the most extreme laboratories to understand accretion and ejection physics to test theories of gravity, according to Sci-News.
There are also stellar-mass black holes aside from supermassive black holes at the center of galaxies. These black holes are mostly discovered when they are in X-ray binaries, which are binary systems that consist of a compact object accreting material from a companion star.
However, if the companion star's mass is lighter than roughly one solar mass, scientists call them low-mass X-ray binaries. On the other hand, a black hole X-ray binary and a neutron star X-ray binary depend on the nature of the central compact object.
MIT astrophysicist Erin Kara and her colleagues said they used X-ray echoes to map a black hole's vicinity. They compared these echoes to the sound echoes used by bats to navigate their surroundings that bounce off an obstacle and return to the bat as an echo.
Similarly, X-ray echoes represent time delays between two types of X-ray light emitted from the corona and from light that bounced off the accretion disk. The time when the telescope receives light from the corona is compared to when it receives X-ray echoes to estimate the distance between the corona and the accretion disk.
Studying this will reveal how the black hole's corona and disk evolve as it consumes stellar material.
"We're at the beginnings of being able to use these light echoes to reconstruct the environments closest to the black hole," the news outlet quoted Kara.
8 Of 10 BlackholeEvolution of X-Ray Echoes Detected
In the study titled "The NICER 'Reverberation Machine': A Systematic Study of Time Lags in Black Hole X-Ray Binaries," published in The Astrophysical Journal, researchers developed a search algorithm that combs through the data in the Neutron star Interior Composition Explorer (NICER) of NASA.
The novel algorithm was able to detect 26 black hole X-ray binary systems that were recorded to have emitted X-ray outbursts, SciTech Daily reported. Out of 26, 10 of these systems were close and bright enough to Earth that scientists could detect X-ray echoes amid the outbursts.
Among the 10 black hole X-ray binaries, eight of them were not previously known. The study's first author and MIT graduate student Jingyi Wang said that they could see new signatures of reverberation in eight sources that vary in mass from five to 15 times the mass of the Sun and are all in binary systems.
Researchers then used their algorithm to check the 10 black hole binaries and divided them into two groups based on their spectral timing and X-ray echoes. The method helped them to quickly track the change in X-ray echoes at every stage of the outburst.
Listen to the converted emission from a typical X-ray echo to audible sound waves below:
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