Peter Clark

'Most massive black hole ever discovered' is detected Astronomers have discovered potentially the most massive black hole ever detected. The cosmic behemoth is close to the theoretical upper limit of what is possible in...

Researchers at the University of Portsmouth and UFRGS in Brazil say the cosmic behemoth is close to the theoretical upper limit of what is possible in the universe and is 10,000 times heavier than the black hole at the centre of our own Milky Way galaxy.

Read more at: ras.ac.uk/news-and-pre...

YouTube video by The News Agents The secret court that silenced the News Agents...until now

Two governments took The News Agents to secret court for two years via a constitutionally unprecedented superinjunction to stop you from hearing this story.

The MoD is responsible for a data leak that put up to 100,000 Afghans at risk of death.

www.youtube.com/watch?v=Zdc6...

AT 2018dyk: tidal disruption event or active galactic nucleus? Follow-up observations of an extreme coronal line emitter with the Dark Energy Spectroscopic Instrument ABSTRACT. We present fresh insights into the nature of the tidal disruption event (TDE) candidate AT 2018dyk. AT 2018dyk has sparked a debate in the litera

At @nam25-durham.bsky.social NAM 2025 in Durham, Claire Greenwell is speaking on "Flipping the switch: what can we learn from the MIR emission of changing-look AGN?". Claire has published in #MNRAS, for example as a co-author on academic.oup.com/mnras/articl...

Congrats Vicky! 😄

An Emerging Risk To #RadioAstronomy 📡

Using a prototype SKA-Low instrument, a new analysis from @icrar.bsky.social has detected Starlink signals leaking into protected radio bands.

@cosmicrami.com writes about this new study.

www.spaceaustralia.com/news/emergin...

📸 Astro_Work 🔭

#SpaceAustralia

Didn't have this level of political chaos on the bingo card today 👀

Thanks for reading!

Very happy to answer any questions you might have on this or the paper itself ☺️

Artist's impression of the WISE spacecraft in orbit. Credit: NASA/JPL-Caltech

MIR observations are a powerful tool in helping to break the degeneracies between these groups.

On a final note, the MIR observations were made by favourite telescope WISE, which was decommissioned and burned up in Earth's atmosphere last year after more than 14 years of data gathering. 🫡

There is a lot more in the paper about the analysis and sample comparisons, but this thread is already feeling like another paper so I will end it here 😅

To conclude!

AT 2018dyk is fascinating TDE that occurred in a gas rich environment.

Telling TDEs apart from AGN flares is *not* an easy job

all had small and relatively 'blue' outbursts.

This is an indication that the different classes of object have environmental differences - perhaps differing amounts of gas/dust or configurations.

I'll be extending and refining this analysis with more objects going forward so stay tuned!

outbursts in the longer wavelength (redder) MIR band tend to be brighter than in the shorter wavelength (bluer) band.

This is also confirmed (those limited by the small number statistics) by those TDEs with redder outbursts also having larger outbursts. Whereas the changing look AGN we explored

I *strongly* advise those interested in the details to read the paper, but in summary.

Changing look AGN outbursts follow a 1-to-1 relation in their peak changes in luminosity in the two WISE bands.
TDEs showing the high energy iron emission lines don't follow this relation. Instead, their

A two panel figure showing the differences in mid-infrared outburst behaviour between TDEs showing high energy emission lines and changing look AGN. Left: Changing look AGN closely follow a 1-to-1 relation between their peak changes in brightnesses in the two WISE bands. TDEs showing high energy emission lines in contrast deviate from this, with their outbursts significantly larger relative to their original brightness in redder of the two bands. Right: Those high energy TDEs showing large outbursts also show redder outbursts in the MIR. This is not the case for AGN.

the MIR behaviour these objects could be used to help tell them apart in a consistent way.

In short - yes it can! Though a lot more work and observations will be needed to tie down the specifics.

Enter this plot:

If this sounds familiar from how the iron and OIII lines are generated, that's because its the same processes involved. Just at a lower energy regime.

As TDEs and AGN related flares are still hard to tell apart - and alas not every galaxy has MaNGA data to help with this - I started to wonder if

in this case is rich in gas because we see a significant flare in the mid-infrared (MIR) at the time following 18dyk's optical detection. Such MIR flares occur when the optical and UV photons thrown out by a TDE get absorbed by nearby material and then reradiated at longer wavelengths over time.

is a less extreme version of this where material at greater distances (or lines of sight) from the SMBH is responding to the increased flux produced by the TDE. We will have to revisit the galaxy in a few more years to see how this emission has evolved.

We also know that the region around the SMBH

TDEs release a lot of high energy photons which can ionise and affect the gas close to the SMBH. We see this in the earlier spectra of 18dyk around its peak brightness which have highly ionised iron emission lines. These lines are only generated in the presence of X-rays.

The delayed OIII emission

This, combined with the new spectrum closely resembling the original SDSS spectrum and with the light-curves (both optical an mid-infrared) of 18dyk behaving in a very transient manner (Flat -> Outburst -> Flat), strongly point to 18dyk being a TDE.

What about the increased OIII emission though? 👀

region of the galaxy each, and all obtained simultaneously.

This allowed us to perform a much more in-depth analysis of how these emission lines are being produced - with this indicating that the emission lines prior to 18dyk being produced by evolved stars rather than AGN activity.

Strong OIII emission is usually a sign of AGN activity, but its more complicated than that as emission lines can be generated my multiple different processes.

To investigate further we also explore archival MaNGA data of the galaxy, which in essence consists of many spectra each covering a small

18dyk's host galaxy doesn't make this easy as its previous (before 18dyk occured) emission line behaviour classifies it as a Low-ionization nuclear emission-line region (LINER) which can be produced by either a relatively 'weak' AGN or emission from evolved stars unrelated to a SMBH.

This shows us that whatever the process that generated 18dyk was, its not an ongoing one, with the host galaxy having returned close to its original state.

I say *close* to because the spectra don't match exactly - the more recent DESI spectrum has much stronger OIII emission than the SDSS spectrum

This spectrum is particularly interesting as we can now explore what the host galaxy is doing now that 18dyk itself has faded away.

We first compared this new spectrum to an archival spectrum obtained by the SDSS years before 18dyk was seen to outburst. With the two looking remarkably similar.

We decided to explore a new spectrum of the galaxy that hosted 18dyk obtained by the Dark Energy Spectroscopic Instrument - DESI which you may be familiar with from its recent cosmology results : newscenter.lbl.gov/2024/04/04/d...

AGNs are similar to TDEs, as they are SMBHs messily 'eating' a load of material, but AGN are fuelled by ongoing processes rather than single events of material in a TDE.

Finally additional analysis reclassified 18dyk back to being a TDE. The confusion coming about by the similar processes in both.

AT 2018dyk has been responsible for quite a lot of confusion over the years. First being classified as a tidal disruption event (TDE: where a star passes too close to a supermassive black hole - SMBH - and gets torn apart), then reclassified as an active galactic nucleus or AGN

AT 2018dyk: tidal disruption event or active galactic nucleus? Follow-up observations of an extreme coronal line emitter with the Dark Energy Spectroscopic Instrument We present fresh insights into the nature of the tidal disruption event (TDE) candidate AT 2018dyk. AT 2018dyk has sparked a debate in the literature around its classification as either a bona-fide TD...

or arXiv if you prefer: arxiv.org/abs/2502.04080

So let's dig in!

Hey everyone! Its time for a paper thread! My first here on Bluesky 😁

This time on the weird and wonderful transient AT 2018dyk 😎

You can read along in this thread, or if you'd prefer to get straight to the paper you can find it ...

Via MNRAS: academic.oup.com/mnras/articl...

Vaccines do not contain any fetal tissue or cells, nor do they contain any cells derived from fetal materials.

Sarah’s rules of looking for life with only chemical signatures:

1) the smaller the molecule(s) the more likely they can also be produced by abiotic processes

2) one molecule, if it can be produced by any abiotic process, will never be enough to definitively claim detection of life