Tag Archives: black hole

Astronomers detect hot gas bubble swirling around the Milky Way’s black hole

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Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have spotted signs of a ‘hot spot’ orbiting Sagittarius A*, the black hole at the centre of our galaxy. The finding helps us better understand the enigmatic and dynamic environment of our supermassive black hole.

“We think we’re looking at a hot bubble of gas zipping around Sagittarius A* on an orbit similar in size to that of the planet Mercury, but making a full loop in just around 70 minutes. This requires a mind blowing velocity of about 30% of the speed of light!” says Maciek Wielgus of the Max Planck Institute for Radio Astronomy in Bonn, Germany, who led the study published today, Sept 22, 2022 in Astronomy & Astrophysics.

The orbit of the hot spot around Sagittarius A*

The observations were made with ALMA in the Chilean Andes — a radio telescope co-owned by the European Southern Observatory (ESO) — during a campaign by the Event Horizon Telescope (EHT) Collaboration to image black holes. In April 2017 the EHT linked together eight existing radio telescopes worldwide, including ALMA, resulting in the recently released first ever image of Sagittarius A.

To calibrate the EHT data, Wielgus and his colleagues, who are members of the EHT Collaboration, used ALMA data recorded simultaneously with the EHT observations of Sagittarius A. To the team’s surprise, there were more clues to the nature of the black hole hidden in the ALMA-only measurements.

By chance, some of the observations were done shortly after a burst or flare of X-ray energy was emitted from the centre of our galaxy, which was spotted by NASA’s Chandra Space Telescope. These kinds of flares, previously observed with X-ray and infrared telescopes, are thought to be associated with so-called ‘hot spots’, hot gas bubbles that orbit very fast and close to the black hole.

The flares were long thought to originate from magnetic interactions in the very hot gas orbiting very close to Sagittarius A*, and the new findings support this idea. “Now we find strong evidence for a magnetic origin of these flares and our observations give us a clue about the geometry of the proces,” says co-author Monika Mościbrodzka from Radboud University.

The observations confirm some of the previous discoveries made by the GRAVITY instrument at ESO’s Very Large Telescope (VLT), which observes in the infrared. The data from GRAVITY and ALMA both suggest the flare originates in a clump of gas swirling around the black hole at about 30% of the speed of light in a clockwise direction in the sky, with the orbit of the hot spot being nearly face-on.

Nobel Prize for Physics, 2017 – Indian Connection

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The 2017 Nobel Prize for Physics has been conferred to three scientists namely Rainer Weiss, Barry C Barish & Kip S Thorne under the LIGO Project for their discovery of gravitational waves, 100 years after Einstein’s General Relativity predicted it. The Nobel Prize for Physics 2017 celebrates the direct detection of Gravitational waves arriving from the merger two large Black holes in a distant galaxy a Billion of light years away. Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained. This opens a new window to Astronomy since Gravitational Waves are an entirely new way of observing the most violent events in space.

This is a proud moment for India also, since the discovery paper has 39 Indian authors/scientists from nine institutions-, CMI Chennai, ICTS-TIFR Bengaluru, IISER-Kolkata, IISER-Trivandrum, IIT Gandhinagar, IPR Gandhinagar, IUCAA Pune, RRCAT Indore and TIFR Mumbai. primarily funded through individual/ institutional grants by Department of Atomic Energy, Department of Science & Technology and Ministry of Human Resource Development AE, DST and MHRD, who are co-authors of this discovery paper.

Late Professor CV Vishveshvara of RRI, Bengaluru (DST AI) and Professor SV Dhurandhar of IUCAA, Pune and some other Indian scientists made seminal contributions to this field which contributed towards the principles behind the LIGO Detector.

The group led by Bala Iyer (currently at ICTS-TIFR) at the Raman Research Institute in collaboration with scientists in France had pioneered the mathematical calculations used to model Gravitational Wave signals from orbiting black holes and neutron stars. Theoretical work that combined black holes and gravitational waves was published by C. V. Vishveshwara in 1970. These contributions are prominently cited in the discovery paper.

An opportunity for India taking leadership in this field has opened up with the LIGO-India mega-science project that was granted ‘in principle’ approval by the Union Cabinet on Feb 17 2016. LIGO-India brings forth a real possibility of Indian scientists and technologists stepping forward, with strong international cooperation, into the frontier of an emergent area of high visibility and promise presented by the recent GW detections and the high promise of a new window of gravitational-wave astronomy to probe the universe.

The global science community is unanimous that the future of Gravitational wave astronomy and astrophysics, beyond the first discovery, lies with the planned global array of GW detectors, including the LIGO-India observatory. Inclusion of LIGO-India greatly improves the angular resolution in the location of the gravitational-wave source by the LIGO global network. For the discovery event observed by the two advanced LIGO detectors in the US, with a hypothetical LIGO-India in operation, there would have been 100 times improvement in the angular resolution.

The LIGO-India proposal is for the construction and operation of an Advanced LIGO Detector in India in collaboration with the LIGO Laboratories, USA. The objective is to set up the Indian node of the three node global Advanced LIGO detector network by 2024 and operate it for 10 years. The task for LIGO-India includes the challenge of constructing the very large vaccum infrastructure that would hold a space of volume 10 million litres that can accommodate the entire 4 km scale laser interferometer in ultra high vacuum environment at nano-torrs. Indian team is also responsible for installation and commissioning the complex instrument and attaining the ultimate design sensitivity.

The LIGO-India project is being jointly executed by lead institutions: the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune of the University Grants commission, and DAE organisations, Institute for Plasma Research (IPR), Gandhinagar, the Raja Ramanna Centre for Advanced Technology (RRCAT), Indore and the Directorate of Construction & Estate Management (DCSEM) of DAE.

LIGO-India is being jointly funded by the Department of Atomic Energy (DAE) and the Department of Science and Technology (DST). A LIGO-India Apex committee, together with the LIGO-India Project Management Board (LI-PMB) and LIGO-India Scientific Management Board (LI-SMB), were constituted in August 2016 to oversee the project execution, and there has been rapid pace of progress since then. LIGO-India is on track for commencing operations by 2024.