Missing Black Holes: In a significant breakthrough, Indian astronomers have traced an intermediate-mass black hole (IMBH) in a faint galaxy approximately 4.3 million light-years away. Using India’s largest optical telescope, they found gas clouds orbiting the black hole at a distance of 125 light-minutes—about 2.25 billion kilometers—with a velocity dispersion of 545 km per second.
This significant discovery, led by astronomers from the Aryabhatta Research Institute of Observational Sciences (ARIES), sheds new light on the growth and interaction of these cosmic “middleweights” that bridge the gap between smaller stellar black holes and supermassive black holes. By employing a sophisticated technique called spectrophotometric reverberation mapping, the team precisely measured the orbital motion of gas clouds around the IMBH, revealing its mass to be approximately 22,000 times that of our Sun.
For decades, scientists have searched for this “missing link” in the black hole family. IMBHs bridge the gap between stellar black holes (a few dozen solar masses) and supermassive black holes (millions to billions of solar masses). Thought to be the seeds from which supermassive black holes grow, IMBHs are hard to detect because of their faint emissions and remote locations in small galaxies.
Led by Shivangi Pandey, a team of researchers from ARIES used the 3.6m Devasthal Optical Telescope (DOT) to detect an IMBH in the galaxy NGC 4395. This low-luminosity galaxy hosts one of the faintest actively feeding black holes ever studied.
To observe and measure it, the team used the DOT’s indigenous spectrograph and camera system (ADFOSC), along with the 1.3m Devasthal Fast Optical Telescope (DFOT), both located at ARIES’ Devasthal Observatory. Given the challenges in resolving such small regions, they applied a sophisticated technique known as spectrophotometric reverberation mapping.
Dr. Suvendu Rakshit, one of the researchers at ARIES, emphasized: “The hunt for more IMBHs is far from over. Larger telescopes and advanced instruments will be key to uncovering these cosmic middleweights.”
This method tracks the time delay between light from the black hole’s accretion disk and the nearby gas clouds (the broad-line region). By monitoring this time lag over two nights using both telescopes, the team was able to determine the size of the emission region and estimate the black hole’s mass.
Key Highlights
- Discovery Location: IMBH found in NGC 4395, a faint galaxy about 4.3 million light-years away.
- Telescope Used: Observations made using India’s largest optical telescope, the 3.6m Devasthal Optical Telescope (DOT), and the 1.3m Devasthal Fast Optical Telescope (DFOT).
- Technique Used: Spectrophotometric reverberation mapping was used to measure time delays in light to determine black hole properties.
- Mass of the IMBH: Estimated at about 22,000 solar masses, making it one of the most precisely measured IMBHs to date.
- Significance of the Discovery: Provides strong evidence for intermediate-mass black holes, which are thought to be the building blocks of supermassive black holes.
- Scientific Validation: Confirms the size-luminosity relationship for black holes in low-luminosity active galaxies.
The team found the IMBH to have a mass of roughly 22,000 times that of the Sun, making it one of the most precisely measured intermediate-mass black holes. It is currently accreting matter at just 6% of its theoretical maximum rate.
Published in The Astrophysical Journal, the study confirms the size-luminosity relationship for black holes in low-luminosity active galaxies, provides a more accurate mass measurement than earlier estimates, and sets a new benchmark for future research.
Dr. Suvendu Rakshit, one of the researchers at ARIES, emphasized: “The hunt for more IMBHs is far from over. Larger telescopes and advanced instruments will be key to uncovering these cosmic middleweights.”
With the rise of more powerful telescopes and imaging technologies, astronomers expect to uncover more IMBHs, helping to complete the picture of black hole growth and galaxy evolution.
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