{"id":13050,"date":"2022-05-16T12:52:28","date_gmt":"2022-05-16T10:52:28","guid":{"rendered":"https:\/\/www.sciencefocus.com\/?p=119404"},"modified":"2022-05-16T13:18:11","modified_gmt":"2022-05-16T11:18:11","slug":"what-you-need-to-know-about-the-sagittarius-a-black-hole-photo","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/rss_feed\/what-you-need-to-know-about-the-sagittarius-a-black-hole-photo\/","title":{"rendered":"What you need to know about the Sagittarius A* black hole photo"},"content":{"rendered":"

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By Sara Rigby\n \t\t<\/p>

Published: Monday, 16 May 2022 at 12:00 am<\/p>

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Last week, on Thursday 12 May, the Event Horizon Telescope Collaboration revealed the first-ever image of Sagittarius A* (Sgr A*), the black hole<\/a> in the centre of our Galaxy, the Milky Way.<\/p>\n

This remarkable image comes three years after the very first image taken of a black hole<\/a>, which shows M87*, the black hole at the centre of the galaxy M87. The two images look similar, despite the differences between the two black holes: at four million times the mass of the Sun, Sgr A* is a thousand times less massive than M87*. Imagine looking for a doughnut on the surface of the Moon from Earth: that\u2019s the amount of area of the sky that Sgr A* takes up.<\/p>\n

The image also represents the most compelling evidence yet that Sgr A* is indeed a supermassive black hole.<\/p>\n

What does the image show?<\/h2>\n

Technically, you can\u2019t take a photo of a black hole itself \u2013 after all, the whole point is that no light can escape. The glowing orange ring in this photo shows the matter surrounding Sgr A*, with the \u2018shadow\u2019 in the centre showing the black hole itself.<\/p>\n

A black hole has an incredibly strong gravitational pull, and will drag any nearby gas and dust into orbit around it. As this material swirls inwards at nearly the speed of light, friction heats it up and it emits energy in the form of radio waves. The Event Horizon Telescope, which detects radio frequencies, picks this up and registers it as a bright halo around the black hole.<\/p>\n

The final image is the result of several individual shots averaged together.<\/p>\n

Where is Sagittarius A*?<\/h2>\n

Sagittarius A* is in the centre of our Galaxy, the Milky Way. From Earth, we can see it in the Sagittarius constellation, and it\u2019s over 26,000 light-years away.<\/p>\n

How does the Event Horizon Telescope work?<\/h2>\n

The Event Horizon Telescope is often referred to as an \u2018Earth-sized telescope\u2019 and as a \u2018virtual telescope\u2019. But what exactly does this mean?<\/p>\n

In astronomy, the bigger the telescope, the better. An amateur\u2019s telescope with a 60mm lens will show you a decent view of the Moon\u2019s surface or even Jupiter and Saturn, whereas the Hubble Space Telescope<\/a>\u2019s 2.4m mirror produces stunning images of nebulae and galaxies<\/a>. Meanwhile, the newly launched James Webb Space Telescope<\/a> has a mirror diameter of 6.5m, and the primary mirror of the upcoming Earth-based Extremely Large Telescope<\/a> is 39 metres across.<\/p>\n

Hubble, James Webb and the ELT are all fantastic feats of engineering, and yet their mirrors are nothing compared to the Event Horizon Telescope. By linking together 11 telescopes around the world, the EHT can effectively create one telescope with a mirror the size of the Earth.<\/p>\n

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The location of Sgr A* in the Milky Way, above the Atacama Large Millimeter\/submillimeter Array \u00a9 ESO\/Jos\u00e9 Francisco Salgado (josefrancisco.org), EHT Collaboration<\/span><\/figcaption><\/div>\n

This virtual telescope is incredibly powerful. It\u2019s the equivalent of sitting in a beer garden in Munich, and seeing the bubbles in a beer glass in New York.<\/p>\n

\u201cWhile the Earth is rotating, all telescopes observe the same astronomical object for several hours,\u201d explained Thomas P Krichbaum<\/a> at the press conference at European Southern Observatory headquarters near Munich. \u201cAt each telescope, the data are recorded on hard disks and are accurately time-tagged by precise atomic clocks. After observations, the data are shipped to processing centres where they are combined in supercomputers.<\/p>\n

\u201cAfter a number of quite complex data analysis steps, this results in the high-resolution image of the radio source.\u201d<\/p>\n

Why did it take so long after the picture of M87*?<\/h2>\n

All the observations for both black hole pictures were done in 2017, so it seems bizarre that it should take up to five years for the public to get to see the images.<\/p>\n

This is because observing through the EHT is not like looking through a reflecting telescope in your garden. What you get back is reams and reams of data that must be analysed and processed before it becomes an image.<\/p>\n

The image of Sgr A* was even harder to produce than the one of M87*. \u201cThe gas in the vicinity of the black holes moves at the same speed \u2014 nearly as fast as light \u2014 around both Sgr A* and M87*,\u201d said Chi-kwan Chan<\/a>, EHT scientist based at the University of Arizona, USA.<\/p>\n

\u201cBut where gas takes days to weeks to orbit the larger M87*, in the much smaller Sgr A* it completes an orbit in mere minutes. This means the brightness and pattern of the gas around Sgr A* were changing rapidly as the EHT Collaboration was observing it \u2014 a bit like trying to take a clear picture of a puppy quickly chasing its tail.\u201d<\/p>\n

\"""\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Map of the telescopes that make up the Event Horizon Telescope \u00a9 ESO\/M Kornmesser<\/span><\/figcaption><\/div>\n

What does this image tell us about the science of black holes?<\/h2>\n

\u201cWe were stunned by how well the size of the ring agreed with predictions from Einstein\u2019s Theory of General Relativity,\u201d said EHT Project Scientist Geoffrey Bower<\/a> from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei. \u201cThese unprecedented observations have greatly improved our understanding of what happens at the very centre of our Galaxy, and offer new insights on how these giant black holes interact with their surroundings.\u201d<\/p>\n

Black holes represent the extremes of what General Relativity can describe, and in the future, the EHT will scour them for the point when the theory breaks down.<\/p>\n

Why is it called Sgr A*?<\/h2>\n

When it was first discovered, astronomers didn\u2019t know what was creating the mysterious radio signal at the centre of our Galaxy. So, due to its location in the constellation of Sagittarius, the radio source was named Sagittarius A.<\/p>\n

Later observations showed that Sagittarius A is actually made up of three components, the most notable of which is the bright, compact object at the centre. Robert Brown, who discovered this particular object with Bruce Balick in 1974, named it Sagittarius A* to distinguish it from Sagittarius A as a whole.<\/p>\n

Brown is said to have chosen the name because the discovery was exciting, and the symbol \u2018*\u2019 is an existing notation in physics to represent an atom in an \u2018excited\u2019 state.<\/p>\n

What\u2019s in the future of the EHT?<\/h2>\n

EHT is in the process of undergoing significant technical upgrades. Observations in March 2022 included more radio telescopes than ever before, and future releases may even include movies of black holes.<\/p>\n

Why is there a supermassive black hole in the centre of the Milky Way \u2013 and should we be worried?<\/h2>\n

Almost every known large galaxy has a supermassive black hole at its centre \u2013 however, it\u2019s not yet known whether galaxies formed around a black hole seed, or whether the centre of the galaxies collapsed into black holes. The existence of supermassive black holes at all is still a mystery: how did they grow to such an enormous size, even in the early Universe?<\/p>\n

Either way, don\u2019t worry: we\u2019re not going to get sucked into Sgr A* any time soon. Black holes don\u2019t \u2018eat\u2019 matter as such \u2013 they just have a lot of mass, so their gravitational pull is particularly strong. We\u2019d orbit around the centre of our Galaxy just the same if the black hole were replaced any other object with the same mass.<\/p>\n

Read more about black holes:<\/strong><\/p>\n