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December 2018: Seeing Double

December 2018

In the show this time, we talk to Amaury Triaud about exoplanets, especially the TRAPPIST-1 system, Fiona Porter rounds up the latest news, and we find out what we can see in the December night sky from Ian Morison and Haritina Mogosanu.

The News

This month in the news: a gamma ray burst candidate, the Sun's long-lost twin, and black holes in virtual reality.

First up, a team led by Joseph Callingham has produced an incredible image of a star system that might produce the closest gamma ray burst ever to be detected. This star system, nicknamed Apep after the Egyptian snake deity of chaos, contains a binary pair of Wolf-Rayet stars. These are massive stars near the end of their lives that have finished burning hydrogen and will eventually become supernovae. In Apep, these stars are orbiting each other at a very high velocity - almost fast enough to tear the stars themselves apart - and producing stellar winds of around 3400 kilometres per second.

It's these winds that have created the most striking feature of Apep: when viewed in the infra-red, pinwheel-shaped trails of dust spiral around the central stars, as can be seen in the image produced by the Very Large Telescope. This sight of a star wrapped by a series of serpentine coils is what led to it being named "Apep", after the mortal enemy of the Egyptian sun god Ra.

Not only is Apep a spectacular sight in itself, but when the stars do collapse to form supernovae, it's believed they might produce a gamma ray burst. Gamma ray bursts are the brightest events in the universe; they involve a strong release of energy at gamma ray wavelengths, which can last between a few milliseconds and a few hours. After the gamma component dies down, they're followed by a longer-lived "afterglow" in longer wavelengths, from X-ray through visible through the radio spectrum.

Gamma ray bursts are, however, quite rare. So far, every burst detected has been outside our galaxy, with the closest to date being around 130 million light years away. Not only is Apep in the Milky Way - the only gamma ray burst source candidate we're found here so far - but it's also only eight thousand light years away. Previously, sources have been too far away to study the stars that created the bursts, so if one does happen, we'll have an unprecedented chance to study its build-up and evolution.

When could we expect to see such a gamma ray burst? The orbital period of the Wolf-Rayet stars helps set a limit. The velocity they're currently moving at can only be maintained for a few hundred thousand years, which is a very short time in astronomy terms, so it could be at any time. In the meanwhile, further observations can help us understand just what's happening in this remarkable system. Callingham et al's paper on Apep may be found here.

Now, from stars very different from our own to one that's very much the same - so much so that it's been described as a solar twin. Discovered by the AMBRE project, a star called HD 186302 has been found to share a large number of characteristics with the Sun. It has very similar chemical abundances, metallicity (which is a measure of elements that aren't hydrogen or helium), temperature, and ratios of carbon isotopes to the Sun, and a spectral type only a few steps away - a G3V or G5V compared to the Sun's G2V.

Most significantly, however, this star's age is very close to the Sun's age, which raises the possibility that they could have the same origins. Rather than being so similar by pure chance, this star and the Sun may have formed in the same stellar nursery over four and a half billion years ago, before the motion of the Milky Way scattered the stars in the nursery. At only 180 light years away, the current location and movements of HD 186302 suggest that it may well be possible these two stars share a common origin.

HD 186302 is only the second solar sibling ever discovered; the first, HD 162826, is around 110 light years away, and it's believed to be unlikely that we'll find any closer to us. Even so, the more of these sibling stars that are found, the more that we'll be able to learn about the Sun's origins. Plans are also now underway to scan HD 186302 to see if it has any planets, and who knows - perhaps it might have one that looks a little bit like the one we live on.

Finally, have you ever wondered what it might look like up close to a black hole? Thanks to a team from Radboud University and Goethe University, you can find out. Using detailed computational models, this group has made a 360 degree virtual reality simulation of the supermassive black hole at the centre of the Milky Way, Sagittarius A*, which can be viewed with any VR console.

As well as allowing for an understanding of the mechanics behind black holes for scientists, the team believes it could serve as a valuable outreach tool, allowing the general public to take a look at these extreme objects. It could also be used as a teaching resource, to help interactively introduce children to the phenomenon of black holes. Even the closest black holes are far away enough that no human today will be able to see one this close in person, but now it's possible to enjoy the sights in the safety and comfort of our own homes.

Interview with Amaury Triaud

Dr. Amaury Triaud (University of Birmingham) talks to us about his research into exoplanetary systems, including the discovery of the TRAPPIST-1 sytem. Also discussed is his work on circumbinary systems, where a planet has two suns, and his observational trips to the Atacama desert. He considers the prospect of life on other planets, and what we might have to look out for in order to discover it.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the Northern Hemisphere night sky during December 2018.

The Planets

Southern Hemisphere

Haritina Mogosanu from the Carter Science Centre in New Zealand speaks about the Southern Hemisphere night sky during December 2018.

Odds and Ends

JBCA PhD student Joe Hanson is part of this year's University of Manchester's University Challenge team, who won their most recent contest to progress to the quarter finals. If you're a Twitter fan, you may have seen that Joe has become a meme superstar as a result of his facial expressions and reactions during the latest contest - video montages have hit the major news outlets. We're sure Joe and the team will go on to win, so stay tuned...

On November 20th 1998, the first module of the International Space Station was launched into orbit, meaning it was recently the ISS's 20th birthday! There was a short delay between this and humans living on-board, but from the 2nd of November 2000 we have had humans living in space orbiting our planet continuously, which is an incredible achievement. The scientific research aboard the ISS is very broad and very fruitful, and we hope this continues long into the future.

We discuss the successful landing of NASA's InSight on Mars, marvelling at just how difficult it would have been and what it had to overcome. Exploring the scientific goals that InSight aims to achieve, we delve into some of the questions that still remain about the red planet - and in the end, does it just boil down to us wanting to find life there?

The Crab pulsar is one of the most observed and studied objects in the sky and is visible at all observable frequencies. It's rotates once every 33.7 milliseconds and is surrounded by the Crab supernova remnant (SNR). The Crab SNR is also a very interesting object, being only one of only nine plerionic SNRs out of the 294 known Galactic SNRs. This episode we discussed Laura's recent paper on some weird scattering effects seen on observations of the Crab pulsar. This type of effect and observation could be a useful tool for telling us more about the Crab SNR and about the interstellar medium (the gas and dust that fills the "spaces" in between objects) between us and the Crab.

Show Credits

News:Fiona Porter
Interview:Amaury Triaud and Emma Alexander
Night sky:Ian Morison, Haritina Mogosanu and Samuel Leske
Presenters:Emma Alexander, Alex Clarke and Laura Driessen
Editors:Adam Avison, George Bendo, Tiaan Bezuidenhout and Tom Scragg
Segment Voice:Tess Jaffe
Website:Jake Staberg Morgan and Stuart Lowe
Producer:Jake Staberg Morgan
Cover art:Top panel: a newly-discovered Wolf-Rayet binary; bottom panel: InSight's first selfie after successfully landing on Mars. CREDIT: Top panel: J. R. Callingham et al., Nature Astronomy; bottom panel: Reuters

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