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 (josefrancisco.org) / 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

UK Space Launch Centres Gain Business

Two space launch centres in the UK have gained further boosts through separate announcements concerning their planned use.

Both announcements came on May 10th, with the first concerning Spaceport Cornwall, in the south-west of the UK mainland. As I’ve previously reported, this is a facility being developed at Cornwall Airport Newquay (CAN) specifically for use by Virgin Orbit and their air-launched LauncherOne rocket, and potentially for Virgin Galactic sub-orbital space tourism flights.

In a joint statement, the US National Reconnaissance Office (NRO) and the UK’s Ministry of Defence (MOD) will inaugurate Virgin Orbit operations with the launch of the Prometheus 2 cubesat system as the primary payload for the launch. Expected to fly later in summer 2022, Prometheus 2 is intended to “provide a test platform for monitoring radio signals including GPS and sophisticated imaging, paving the way for a more collaborative and connected space communication system.”

The agreement marks the first time the highly-secretive NRO (responsible for operating the US fleet of spy satellites) will use a horizontal launch system for a mission, and also marks a further expansion of the agency’s desire to be able to deploy satellites into a range of orbits from launch facilities around the world, having also reached an agreement to fly missions out of New Zealand as well.

Virgin Orbit’s Cosmic Girl aerial launch platform and its LauncherOne rocket will fly a joint US NRO / UK MOD satellite to orbit as the primary element of its first operational launch from UK soil. Credit: Virgin Orbit

Meanwhile Astra Aerospace, the US-based commercial launch service (which became famous in 2021 when one of its launch vehicles got a little existential, going sideways across the launch pad for around 20 seconds after engine ignition before it decided going vertical might be the better option after all), plans to start carrying out launches from Scotland in 2023.

Already specialising somewhat in providing launches to polar orbit out of Alaska, Astra has indicated it plans to offer a similar launch service for European customers out of the proposed SaxaVord Spaceport, to be located on the Lamba Ness peninsula on Unst, the most northerly of the Shetland Islands.

Originally proposed as the Shetland Space Centre, SaxaVord was one of two Scottish launch centres seeking UK government funding, the other being the Sutherland Space Hub, located on the northernmost coast of the Scottish mainland. Whilst the Shetland propose did gain both government and venture capital funding, it ground to a halt when Historic Environment Scotland (HES), a statutory body, refused consent for the development as it would destroy a scheduled monument of national significance, really leaving only the Sutherland proposal in the running.

An artist’s impression looking south over the Lamba Ness peninsula, Isle of Unst, showing the proposed launch pad in the foreground with a launch vehicle lifting off and launch processing and control facilities in the background. Credit: SaxaVord Spaceport

More recently, however, HES has removed its objections to the SaxaVord development, allowing it to proceed to a point where construction is due to start in summer 2022. And in a reversal of fortunes, the Sutherland development has run into problems.

The largest of these are the planning / operating restrictions placed on the site; the former limits it to just one launch pad – two were originally proposed, each with its own launch capabilities -, while the latter limits the total number of launches from the site to just 12 a year. These limitations have already seen one of the two users of the Sutherland site, Lockheed Martin, withdraw from the site in favour of SaxaVord.

China Confirms Space Telescope to Launch in Late 2023

China has confirmed it plans to launch the next major element of its expanding space programme in late 2023, when a Long March 5B booster will carry the Xuntian space telescope into orbit.

Some outlets have – incorrectly – compared Xuntian (“Space Sentinel”) with NASA’s James Webb Telescope (JWST). However, given its capabilities, the telescope is more akin to the NASA / ESA Hubble Space Telescope (HST), although it will have a degree of overlap with JWST when it comes to infra-red observations.

Like Hubble, Xuntian – also referred to as the China Space Station Telescope (CSST) – will primarily operate in the visible light spectrum, with a primary mirror 2 metres in diameter (compared to Hubble’s 2.4 m). It will have an all-up weight of around 15.5 tonnes (compared to Hubble’s 11.1 tonnes), and also like Hubble, it will be made available for international deep space and cosmological studies.

An artist’s impression of Xuntian, the China Space Station Telescope (CSST). Credit: Jaimito130805, CC BY-SA 4.0

Also like Hubble, CSST will also be serviceable once in orbit – but in a rather novel way. When first announced, the telescope was going to be attached to China’s Tiangong space station. However, to avoid issues of contamination / damage as a result of station operations, CSST will now be free-flying, but occupying the same orbit as the space station, but a few kilometres away from it. When servicing is required, the telescope will manoeuvre to Tiangong and dock with it, allowing its fuel reserves to be topped-up and the station crew to perform any required repairs / upgrades.

The key differentiators between CSST and Hubble is that the CSST will be a Cook-type, off-axis observatory, allowing it to manage higher levels of precision in photometry, position, and shape measurements than can be achieved by Hubble, and while its primary mirror is slightly smaller, its more modern optic and imaging system will give it a field of view up to 300 times larger that HST, allowing it to undertake a broader range of observations.

Once launched, CSST will go through several months of commissioning period to starting operations in around mid-2024. Its primary mission has been set for 10 years, but thanks to the servicing capability, it could last well beyond that.

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