{"id":29873,"date":"2022-03-14T14:41:09","date_gmt":"2022-03-14T14:41:09","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=105992"},"modified":"2022-03-14T14:56:13","modified_gmt":"2022-03-14T14:56:13","slug":"our-galaxys-central-black-hole-erupts-unpredictably-and-chaotically","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/our-galaxys-central-black-hole-erupts-unpredictably-and-chaotically\/","title":{"rendered":"Our Galaxy\u2019s central black hole erupts unpredictably and chaotically"},"content":{"rendered":"

<\/p>

By Chris Lintott\n \t\t<\/p>

Published: Monday, 14 March 2022 at 12:00 am<\/p>

\n\n

Known as Sagittarius A* (Sgr A*), the black hole<\/a> at the centre of our Galaxy lies more than 26,000 lightyears from Earth, and is around four million times the mass of the Sun.<\/p>\n

Sgr A* was discovered by astronomers Bruce Balick and Robert L. Brown, who revealed in a 1974 science paper that they had discovered a bright radio source at the centre of the Milky Way.<\/span><\/p>\n

The hot gas and dust around the black hole means it glows brightly at radio, X-ray and gamma ray wavelengths.<\/p>\n

Read our answers to some of the biggest questions about black holes<\/a>.<\/strong><\/em><\/p>\n

\""The\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
The centre of the Milky Way, as seen by the Spitzer Space Telescope. Credit: NASA, JPL-Caltech, Susan Stolovy (SSC\/Caltech) et al.<\/span><\/figcaption><\/div>\n

Astronomers have known for decades that over the timescale of a day the emissions will suddenly flare, increasing in brightness by ten to a hundred times, but weren\u2019t sure how this flaring behaved over longer time spans.<\/p>\n

Recently, astronomers have discovered that Sagittarius A* erupts unpredictably and chaotically, using over 15 years of data on the black hole.<\/p>\n

\""A\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
A collection of black holes near the centre of the Milky Way, just 3 lightyears from Sagittarius A*, captured by the Chandra X-ray Observatory. Credit: NASA\/CXC\/Columbia Univ.\/C. Hailey et al.<\/span><\/figcaption><\/div>\n

Alexis Andr\u00e9s is a postgraduate student from the University of Amsterdam. He looked at data taken by the Neil Gehrels Swift Observatory, a telescope that has been looking for gamma ray bursts<\/a> since 2006.<\/p>\n

\u201cThe long dataset of the Swift Observatory did not just happen by accident,\u201d says Nathalie Degenaar, who requested the specific measurements from Swift when she was a PhD student and became Andr\u00e9s\u2019s supervisor at the University of Amsterdam.<\/p>\n

\u201cSince then, I\u2019ve been applying for more observing time regularly. It\u2019s a very special observing programme that allows us to conduct a lot of research.\u201d<\/p>\n

This data showed that Sgr A* had a high rate of flares from 2006 to 2008, which then dropped off before rising once again in 2012.<\/p>\n

\""A\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
A Hubble Space Telescope image showing a number of galaxies thought to host bright gamma-ray bursts. Credit: NASA, ESA, A. Fruchter (STScI), and the GOSH Collaboration<\/span><\/figcaption><\/div>\n

\u201cHow the flares occur remains unclear,\u201d says Jakob van den Eijnden from the University of Oxford.<\/p>\n

\u201cIt was previously thought that more flares follow after gaseous clouds or stars pass by the black hole, but there is no evidence for that yet.<\/p>\n

\u201cAnd we cannot yet confirm the hypothesis that the magnetic properties of the surrounding gas play a role either.\u201d<\/p>\n

The team hope to uncover more about the flare\u2019s changing rate by monitoring Sgr A* using Swift over the next few years.<\/span><\/p>\n

This <\/span>should reveal whether a passing cloud or an as yet unknown phenomenon is causing <\/span>this fitful behaviour at our Galaxy\u2019s heart.<\/p>\n

This article originally appeared in the March 2022 issue of <\/strong><\/em>BBC Sky at Night Magazine<\/strong>.<\/strong><\/em><\/p><\/body><\/html>\n

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