May 2020: Breaking Apart

In the show this time Emma Alexander rounds up the latest news, and we find out what we can see in the May night sky from Ian Morison, Haritina Mogosanu and Samuel Leske.

The News

This month in the news: A potentially groundbreaking fast radio burst detection, the breakup of comet Atlas and the disappearing exoplanet Formalhaut B

First up: a potentially very exciting Fast Radio Burst, or FRB. Fast Radio Bursts are exactly what they say on the tin: a strong, transient radio signal, lasting a short amount of time. The first FRB was discovered in 2007 from archive data, so is still a relatively new field in astronomy. Although telescopes were detecting these bursts, it wasn’t clear what was causing them astrophysical. They had to have occurred outside our own galaxy, and must be very powerful. At one point, it was said that there were more theories about what FRBs are than there were detected FRBs! FRB detections are now coming in thick and fast as there are more projects and equipment dedicated to studying them. These detections now include repeating fast radio bursts, and with repetition came localisation & host galaxy identification. But it was still unclear what was causing them.

A newly detected FRB might start to shed some light on them however. Now, I will start this news item with the disclaimer that this is all very new, and although it is possibly something to be excited about, it is also still early days. On the 27th April 2020, a range of gamma ray and X-ray telescopes detected a burst from the Soft Gamma Repeater SGR 1935+2154, a known magnetar 30,000 light-years away in our own Milky Way Galaxy. Magnetars are neutron stars with extreme magnetic fields: small in size, but incredibly energetic. Their extreme magnetic fields can distort their shape, creating a tension with the inwards gravitational pull and causing flares. They’re one of the types of astrophysical objects or events theorised to cause fast radio bursts, but in this case, everything looked like a typical magnetar gamma ray burst. Fast Radio Bursts had only ever been detected in radio waves, and never associated with any more higher frequency emission.

However, the next day, 28th April, CHIME, the Canadian Hydrogen Intensity Mapping Experiment, recorded an FRB coming from the same direction as the magnetar. Because the FRB was detected in multiple beams of the telescope, its could be pinpointed on the sky. Also, the Dispersion Measure of the FRB, which characterises how the signal is spread over time at different frequencies, and is indicative of how much “stuff” it has travelled through to get to us, puts it within the distance of our Milky Way Galaxy, a first for FRB detections. CHIME reported their detection in the Astronomer’s Telegram, and was followed up by the reporting of a second, independent detection of the FRB. This independent detection was made by STARE2: a set of 3 radio feeds located in California and Utah spread between 600km. It was designed to detect local FRBs, which we will see much brighter than extragalactic ones due to their proximity, and to be able to locate them. STARE2 did report a fluence (a measure of brightness and duration of the burst) 1000 times greater than CHIME, so the detections aren’t completely consistent as they are currently reported. At its peak, the burst could have been one of the brightest radio sources in the sky, comparable to Cassiopeia A and Cygnus A.

So, what do we know for sure? One of the possible theorised origins of Fast Radio Bursts are magnetars. A magnetar in our own Milky Way Galaxy showed a burst of activity, and subsequently a Fast Radio Burst was detected coming from the same region of sky. It’s too early to confidently link all of these things, but follow up observations have been encouraged and we should hopefully know more details when full publications are released. If there is a link, it would be revolutionary within the FRB field.

Next up: Hubble witnesses the demise of comet ATLAS (formal designation C/2019 Y4). The space telescope imaged the comet to find it had broken into pieces. Discovered on the 29th Dec 2019 by the Asteroid Terrestrial-impact Last Alert System, or ATLAS, the comet had been closely anticipated by many astronomers. At one point, its brightening suggested that it could become visible to the naked eye on its closest approach to Earth later this month, and be one of the brightest comets of the past two decades. Now, the once football field sized body has broken up into smaller pieces, with the biggest estimated to be the size of a house. Although this may be a disappointing event for many, it provides an exciting insight into comet fragmentation — with comets bright enough to be observed typically only breaking up once or twice a decade. Definitely something to celebrate as Hubble reaches its 30th anniversary in space! You can view the images of comet ATLAS , and other content celebrating Hubble’s birthday online.

The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the Northern Hemisphere night sky during May 2020.

Southern Hemisphere

Haritina Mogosanu and Samuel Leske from the Carter Science Centre in New Zealand speaks about the Southern Hemisphere night sky during May 2020.

Show Credits