Space Sunday: black holes, UK launches & a Chinese sentinel

An image of the super-massive black hole (SMBH) at the centre of our galaxy, as released by the Event Horizon Telescope (EHT) team, May 12th, 2022. Credit: European Southern Observatory (ESO) / EHT

On Thursday May 12th, 2022, the consortium of global observatories that calls itself the Event Horizon Telescope (EHT) announced it had successfully imaged the super massive black hole (SMBH) residing at the centre of our galaxy. It’s not the first time such a SMBH has been imaged – EHT captured the first direct look at one back in 2019, when it observed the black hole at the centre of the supergiant elliptical galaxy Messier 87 (M87*, pronounced “M87-Star”) 55 million light years away, but is still a remarkable feat.

Sitting at the centre of our galaxy and a “mere” 27,000 light years from Earth, Sagittarius A* (pronounced “Sagittarius A Star” or Sgr A*, and so-called because it lies within the constellation of Sagittarius close to the boundary with neighbouring of Scorpius when viewed from Earth) is some 51.8 million km in diameter and has an estimated mass equivalent to 4.154 million Suns.

A composite image showing three of the radio telescopes in the European Southern Observatory’s Atacama Large Millimeter/submillimeter Array (ALMA), Chile, aimed towards the heart of our galaxy and the location of Sgr A*  (image inset). Note the fourth telescope in the background of the image is not aimed at the same point. Credit: ESO/José Francisco Salgado ( / EHT

Because of its distance and size (in terms of SMBHs, it is actually fairly middling (M87*, by comparison has a mass somewhere between 3.5 and 6.6 billion Suns) and factors such as the volume of natural light and interstellar dust between Earth and Sqr A*, we cannot see it in the visible light spectrum.

However, we can detect the infra-red radiation from the space around it. This is important because black holes are surrounded by an accretion disk – material attracted by the gravity well of the black hole and which fall into an orbit around it just beyond the event horizon. This material is travelling as such massive speed, it creates high-energy radiation that can be detected.

Even so, gathering the necessary data to image an SMBH, even one as relatively close to Earth as Sgr A* or as incredibly huge as M87* (which is thousands of times bigger than Sgr A*) requires an extraordinary observation system. Enter the Event Horizon Telescope (EHT).

This is actually a network of (currently) eleven independent radio telescopes around the world. It extends from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany, and the Very Long Baseline Array (VLBA) in New Mexico, USA, down to the South Pole Telescope (SPT) located at the Amundsen–Scott South Pole Station, Antarctica; and from the James Clerk Maxwell Telescope and the Submillimeter Array, Hawaii to the Northern Extended Millimeter Array on the Plateau de Bure in the French Alps.

The EHT network of observatories. Credit: ESO / EHT via Wikipedia

Together, the telescopes work like this: as the Earth spins, the target object rises over the horizon for some of the telescopes, they all lock onto it with millimetre precision, and track it across the sky. As more telescopes in the network are able to join in, they do, while those passing beyond the point where they can see the target cease observations until the Earth’s rotation brings the object back into view.

This effectively turns Earth itself into a massive radio telescope using Very Long Baseline Interferometry (VLBI), with all of the telescopes gathering an immense amount of data at resolutions far in excess of anything the individual telescopes could achieve. So much data, in fact, that the images of Sgr A* released by the EHT actually don’t do genuine justice.

This is because the total amount of image data gathered by EHT amounts to 3.5 petabytes (that’s equivalent to 100 million Tik Tok videos for the young ‘uns out there!). In order to produce images that could be easily transmitted over the Internet, this data had to be compressed and altered. In fact, the data volume was so huge, it was easier to remove the hard drives containing it and shipping them to the various centres around the world wanting to analyse the data, rather than trying to transmit the data between different locations!

The data were gathered over the course of multiple nights of observations performed by the telescopes in the network in 2017, and it has taken 5 years of analysis using a batch of super computers for the researchers to reach a consensus. This was in part due to the nature of Sgr A* itself. The EHT team had cut their teeth observing M87*, but in terms of imaging, Sqr A* is completely different, as EHT team member Chi-kwan Chan explains:

The gas in the vicinity of the black holes moves at the same speed – nearly as fast as light – around both Sgr A* and M87*. But where gas takes days to weeks to orbit the larger M87*, allowing us to gather consistent images over days. The material around 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 we were trying to image it, so it was a bit like trying to take a clear picture of a puppy quickly chasing its tail.

– Chi-kwan Chan, Steward Observatory, University of Arizona

However, one thing did emerge as processing continued: despite being very different in almost every respect, both M87* and Sgr A* have produced images that are remarkably similar. That they do is seen as a further proof of Einstein’s theory of general relatively, with both accretion disks conforming to his predictions of what should be seen, despite the – no pun intended – massive differences in their nature.

And that’s the key factor in studies like this: they do much to help increase / confirm our understandings of the cosmos around us (or at least, reveal what we theorise to be the case is actually the case). With M87* and Sgr A*, the data gathered are allowing scientists to formulate and model a “library” of different simulated black holes. This library in turn enables researchers test the laws of physics under different domains and offer opportunities to better understand the formation, life and death of galaxies and the very nature of SMBHs themselves, which are believed to be the “powerhouses” of massive galaxies.

Despite being – quite literally – massively different and exhibiting very different natures, when imaged in the infra-red, M87* (55 million light years away at the heart of the M87 galaxy) and Sgr A* (27,000 light years away at the heart of our galaxy) produce remarkably similar images, both of which conform to Einstein’s theory of general relativity. Credit: ESO / EHT

One of the things the EHT observations of Sgr A* have confirmed is that it is actually quite “tame”. In contrast to the idea of the black hole “sucking in” any and all material straying too close to it, it does nothing of the sort – and this appears to be typical for black holes of all sizes.

If Sagittarius A* were a person, it would consume a single grain of rice every million years. Only a trickle of material is actually making it all the way to the black hole. Sagittarius A* is giving us a view into the much more standard state of black holes: quiet and quiescent. M87 was exciting because it was extraordinary in size and power. Sagittarius A* is exciting because it’s common.

– Michael Johnson, Harvard/Smithsonian Centre for Astrophysics

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2022 Raglan Shire Artwalk in Second Life

Raglan Shire Artwalk 2022

Raglan Shire, Second Life’s Tiny community, has once again opened its doors to people from across the grid as participating artists and visitors are invited to the Raglan Shire Artwalk 2022.

This year, the the event runs from Sunday, May 15th, through until Sunday, June 19th, 2022. It  offers an opportunity not just to appreciate a huge range of art from both the physical and digital worlds, but to also tour the Shire regions and enjoy the hospitality of the Raglan Shire community.

A non-juried exhibition, the Artwalk is open to any artist wishing to enter, and has minimal restrictions on the type of art displayed (one of the most important being all art is in keeping with the Shire’s maturity rating). All of this means that it offers one of the richest mixes of SL art displayed within a single location in Second Life, with 2D art is displayed along the hedgerows of the Shire’s pathways and tree platforms overhead and 3D art among the community’s parks.

Raglan Shire Artwalk 2022: Marcel Mosswood and Barry Richez

Each year attracts well over a hundred SL artist – and this year is no exception. The depth and range of art on display is guaranteed to keep visitors exploring the paths and walks around the through the hedgerows – and if walking proves a little much, there are always the Shire’s tours to ease the load on the feet.

Also, teleport boards are provided to help people find their way around the exhibition spaces. However, given this is an opportunity to visit and appreciate Raglan Shire, I do recommend exercising your pedal extremities and doing at least some of your exploration on foot – just keep in mind people do have their homes in the regions as well.

Given the number of artists involved, there isn’t a published list of participants, but anyone interested in the world of SL art is bound to recognise many of the names of the artists here. The Artwalk is also a marvellous way to see art from both our physical and digital worlds and for catch artists both familiar and new to your eye. Just don’t try to see it all at once; the Artwalk is open for a month, which gives plenty of time for browsing and appreciating the art without feeling overloaded.

Raglan Shire Artwalk: someone called “Pey” … 🙂

SLurl Details

All of the Raglan Shire Artwalk regions are rated General)