Space Sunday: black holes, Falcons and moonshots

The first ever direct image of a black hole: M87* at the heart of the galaxy M87, 55 million light years from Earth, released on April 10th, 2019. Credit: the EHT Collaboration

The black hole in the above image resides at the centre of Messier 87 (M87), around 16.4 million parsecs (53 million light-years) from Earth, and part of the Virgo galactic cluster of about 12,000 galaxies. It marks the first time we have directly imaged a black hole – and it is a remarkable achievement for a number of reasons.

Thanks to Hollywood, we’re all very probably familiar with the idea of black holes: a point is space where matter is so compressed that it creates a gravity field from which not even light can escape. However, black holes come in a variety of forms, of which the most unusual might well be those that exist at the centre of many galaxies – including our own. Referred to as “supermassive black holes” on account of their extreme mass, they on a scale many times larger than your typical stellar black hole (which, despite being referred to as “massive” – a reference to their gravitational attraction.

Left: M87 in the Virgo cluster of galaxies, as imaged by the European Southern Observatory’s Very Large Telescope. Note the 5,000 light year-long jet of gas (arrowed) rising from the galaxy. Right: a closer view of M87 and the gas jet captures by the Hubble Space Telescope. Extending well beyond the galaxy, and move at relativistic speeds, the jet is believed to be generated by the black hole at the heart of the galaxy. Credits: ESO (l); J. A. Biretta et al., (STScI /AURA), NASA

We don’t actually understand how galactic black holes like the one at the heart of M87 – and called M87*) formed, but being able to examine them directly could answer some fundamental questions about the nature of the universe and physics, as well as helping us to understand the role they play in the evolution of galaxies. The problem is, actually directly imaging any black hole is actually very hard simply because they are – well, black, and thus not the easiest of things to see against the blackness of space.

Fortunately, there is a way around this problem: black holes are not alone. Their massive gravity means they attract dust and gas, which forms an accretion disk around the black hole, spinning around them at enormous speeds and producing radiation in a range of wavelengths including radio, optical and infra-red. Given given the right capabilities, we can image a black hole against the radiation from this accretion disk.

The composition of a black hole. Credit: ESO, ESA/Hubble, M. Kornmesser/N. Bartmann

But even with an accretion disk to shed light around a galactic black hole has its own set of issues. To image the one at the centre of our own galaxy, for example, is the equivalent of trying to stand in New York’s Times Square and being able to count the dimples on a golf ball 4,000 km (2,450 mi) away; and this despite the fact that the black hole at the centre of our galaxy is thought to be at least 60 million kilometres across.

Nor is trying to image them optically particularly helpful. They need to be imaged across a range of wavelengths – the problem here being that to do so, you need a radio telescope effectively the size of the Earth.

To achieve this, and following an idea first put forward 26 years ago by German radio-astronomer Heino Falcke, the idea of the Event Horizon Telescope (EHT) was developed. This involves linking numerous radio telescopes together so they can jointly examine a single target and gather data on it.

To image M87*, eight of the world’s most powerful radio telescopes and telescope arrays were linked together. Over a period of about a week in 2017, they were used to gather 4 petabytes of data about the light from M87* in the millimetre wavelength. The drives containing this data were then physically shipped from the observatories to the Haystack Observatory and the Max Planck Institute for Radio Astronomy, where they were plugged into a  grid computer made from about 800 CPUs linked through a 40 Gbit/s network, with the data processed by four independent teams using a series of tested algorithms to ascertain the reliability of the results. The final processing run was completed using the two most established algorithms to produce the image seen here.

This is in fact only the first galactic black hole image to b released. As well as studying M87*, the global EHT array has also gathered data on the black hole at the centre of our galaxy (and called Sagittarius A*), and at least two other supermassive black holes. However, imaging our own galactic black hole proved much harder, and delays in getting the physical hardware containing the data captured by the South Pole Telescope shipped from Antarctica to the Haystack Observatory has  meant that processing the data is still in progress.

According to theoretical physics – such as Einstein’s theory of relativity – scientists already knew what the image should look like: the aforementioned glowing accretion disk and the shadow of the black hole at its centre (so beloved of sci-fi films that feature black holes). However, simply seeing an image that matches what we believe we should be theoretically seeing helps further confirm Einstein’s theories about the nature of the universe around us.

Theoretical physics, such as Einstein’s general theory of relativity, had given scientists a means of simulating what an image of a black hole might look like, as with the above picture of M87*, released by the EHT team in April 2017 as they were about to commence their data gathering. Credit: Bronzwaer/Davelaar/Moscibrodzka/Falcke, Radboud University

From the actual image on M87*, scientists have already been able to confirm Einstein’s general theory of relativity under extreme conditions – notably the prediction of a dark shadow-like region, caused by gravitational bending and capture of light. They have also confirmed the shadow is consistent with expectations for that of a spinning Kerr black hole, which Einstein again predicted. Further, by combining the asymmetric nature of the accretion disk with the angle of the relativistic plasma jet created by M87* (not actually visible in the black hole image), astronomers believe M87* is spinning in a clockwise direction.

Further, the image has refined estimates of M87*’s size – 40 billion km across the event horizon (that’s 270 AU or 0.0042 light years; roughly 2.5 times smaller than the shadow circle shown in the image) – and its mass, estimated at 6.5 billion solar masses (± 0.7 billion).

We have taken the first picture of a black hole. This is an extraordinary scientific feat accomplished by a team of more than 200 researchers.

– Sheperd S. Doeleman, EHT project director

The image itself is shown in false colour to indicate the intensity of the emissions from the accretion disk. Yellow represents the most intense emissions, dropping to red as the lower intensity emissions, and black for little or no emissions. Were we able to see M87* with the naked eye, the colours would lightly be white, perhaps slightly tainted with blue or red. And while it has yet to be 100% confirmed, the colour bias towards yellow on the southern arc of the ring, together with its asymmetry, is thought to be the result of the gases in that region moving more in our general direction.

While this image has already revealed much, there are numerous questions we have yet to fathom. We may now know the nature of M87*, but we still don’t know how it was formed, or why so many galaxies have black holes at their centres. Nor do we as yet understand why some (like M87*) produce the great plumes of relativistic gas while others, such as the black hole at the centre of our galaxy do not.  So expect more to come as a result of studies arising from the work of EHT.

Beresheet Lost

Launched on February 21st, Israel’s Beresheet lunar lander mission, was lost as it attempted to make its Moon landing on April 11th.

The vehicle, originally built by the SpaceIL team to compete in the (ultimately cancelled) Google Lunar X-Prize, was attempting to land in the Mare Serenitatis region of the Moon, having spiralled its way from Earth to lunar orbit during March, and then spending a week orbiting the Moon.

Initially, things went well with the landing: the main engine fired, slowing the vehicle sufficiently to start its decent, and Beresheet returned an image of its landing region from an altitude of 22 km.

An image from SpaceIL’s Beresheet lander taken during its landing attempt at an altitude of about 22 km. Credit: SpaceIL

However, at 14 km above the Moon’s surface, the lander began to suffer what SpaceIL later referred to as a “chain of events” that resulted in the vehicle’s loss. These started with a problem with an inertial measurement unit on the spacecraft (which was noted by mission control during the descent) and culminated in an initial failure of the vehicle’s main engine to restart in order to slow its final descent and cushion the landing. While the motor was successfully restarted, it was too late. The final telemetry received from Beresheet indicated that at a height of 150m above the Moon, it was descending at 500 km/h – much too fast for a controlled soft landing.

But this is not game over for SpaceIL. Following the cancellation of the Google Lunar XPrize, the company teamed with Israel’s government-owned aerospace company Israel Aerospace Industries to complete the project, and both have already confirmed they will be trying again.

We’re going to actually build a new halalit –  a new spacecraft. We’re going to put it on the moon, and we’re going to complete the mission … The work on Beresheet 2.0 will begin immediately. The team is meeting this weekend to start planning the new project.

– Billionaire Morris Kahn, SpaceIL Chairman

The last image returned by Beresheet before it smashed into the surface of the Moon at around 500 km/h

That work is liable to involve a comprehensive post-mortem on the original mission, not just because of the final failure, but because Beresheet suffered multiple issues during its six-week voyage from Earth to the Moon – all of which it recovered from, but which may have been the results of compromises inherent in the design as a result of it taking a piggyback ride into orbit aboard another mission. In the meantime, the X-Prize organisation offered a small sweetener to SpaceIL: a US $1 million bonus award.

I think they managed to touch the surface of the moon, and that’s what we were looking for [with] our Moonshot Award.

– X-Prize CEO Anousheh Ansari

Beresheet’s loss sits as a reminder that landing on the Moon isn’t necessarily easy – something NASA planners will likely be keeping in mind given the pressure they are under to return humans to the surface of the Moon by 2024, and yet to have a confirmed method (and vehicle) capable of doing so.

Falcon Heavy Thunders

The Block 5 Falcon Heavy thunders into the sky on April 11th, 2019 from Kennedy Space Centre’s Pad 39A, carrying the Arabsat 6A communications satellite to orbit

On Thursday, April 11th, 2019, SpaceX completed the second launch of its mighty Falcon Heavy rocket. It was something of a milestone in the vehicle’s evolution, being its first commercial launch, and the first with the rocket in its “Block 5” configuration, using the cores stages from the most powerful variant of the Falcon 9 booster.

The launch was a resounding success on all fronts: following a picture-perfect lift-off, the vehicle climbed to “first stage” separation – the point at which the two Falcon 9 side boosters separated, leaving the central core stage pushing the upper stage and its 6.4-tonne Arabsat 6A communications satellite towards orbit. The two side boosters they performed their “burn back” manoeuvres, flying back to Florida to make near synchronous landings at Cape Canaveral Air Force Station 8 minutes after launch.

Touchdown! The two Falcon 9 boosters land at Cape Canaveral 8 minutes after the Falcon Heavy launch on April 11th, 2019. Credit: NASA / SpaceX

Following its separation two minutes after the side boosters, the core stage also made a burn back manoeuvre but, having travelled a much greater distance, descended to make a successful landing on the autonomous drone ship Of Course I Still Love You, almost 1,000 km off the Florida coast. This marked another first for SpaceX: the recovery of all three core stages from a single launch (the core stage used for the vehicle’s test flight in February 2018 failed to make a successful at-sea landing).

Nor did it end there. Following their jettisoning from the upper stage and satellite, the rocket’s payload fairings fell back to a watery landing at sea, and were safely recovered.

One of the two Falcon Heavy payload fairings aboard a recover ship after splashing down in the Atlantic. Credit: SpaceX

With successful delivery of  Arabsat 6A to orbit, SpaceX indicated that the two Falcon boosters will be re-used on the next Falcon Heavy mission, the launch of the US Air Force / NASA STP-2 flight in June, while the payload fairings will be used on a Falcon 9 launch of more of the company’s Starlink global broadband satellites.

The “Roc” Flies

On Saturday, April 13th, Stratolaunch, the private launch company founded by the late billionaire Paul Allen, successfully completed the first flight of the world’s largest aircraft by wingspan.

Dubbed the “Roc”, the Scaled Composites Model 351 is a six-engined, “twin-hulled” behemoth, designed to be an aerial launch platform for up to three Pegasus XL rockets per flight. Originally rolled-out in March 2017, the aircraft has more recently completed several months of taxi tests, which included “rotation authority manoeuvres”, design to simulate everything up to the point of take-off.

The first flight for the aircraft, which uses two heavily modified 747 fuselages, commenced as it rolled down the runway at Mojave Air and Space Port in California at 06:58 local time and completed a full rotation. Lifting clear of the runway, the “Roc” entered a 2.5 hour test flight and reached an altitude of 4,570 m (15,000 ft), before returning to base and making a perfect landing.

I honestly could not have hoped for more on a first flight, especially of an aeroplane of this complexity and this uniqueness. Really, for a first flight, it was spot on.

– Evan Thomas, Scaled Composites test pilot, after the flight

Despite the success of the flight, Stratolaunch has refused to comment on when “Roc” might next take to the air. There are also questions on the viability of the system. While Stratolaunch have settled on the idea of carrying three Pegasus XL launch craft per flight, the Pegasus programme has itself struggled to win customers in recent years. As such, doubts exist about the cmpany’s ability to attract either commercial or military customers.

2 thoughts on “Space Sunday: black holes, Falcons and moonshots

    1. Yup. And the black hole at the centre of our galaxy is believed to be 60 billion km across – half as big again as M87*. So imagine a “shadow” that is 2.5 times bigger than that 🙂 .

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