An impending supermassive black hole merger

[robin_astro]

According to a paper published last week the 17th magnitude Seyfert Galaxy  SDSSJ1430+2303/ (seen here in my spectrograph guider last night)

contains a pair of supermassive black holes who's orbit is rapidly decaying and which are likely to merge in the next 3 years or possibly even sooner in just 100-300 days time. My spectrum (blue, overlaid on the latest spectrum in the paper in grey and corrected for the redshift) shows Hydrogen alpha emission at velocities up to +-12000km/s 

More on my BAA page here

https://britastro.org/observations/observation.php?id=20220207_205606_9d5b2259183a3d41

Cheers

Robin

[markse68]

Hi Robin, what does it mean “Hydrogen alpha emission at velocities up to +-12000km/s ” and what does it infer?

Mark

[robin_astro]

42 minutes ago, markse68 said:

what does it mean “Hydrogen alpha emission at velocities up to +-12000km/s ” and what does it infer

Hi Mark,

Most if not all galaxies have a supermassive black hole at their centre and if there is material nearby (dust, gas and even the odd star) it forms a disc and the  material heats up as it spirals in producing emission at the Hydrogen alpha wavelength. (these galaxies are termed as having  "Active Galactic Nuclei"   Quasars and Seyfert Galaxies are examples of these. You can see this effect in this spectrum of M87, the black hole of which was famously imaged a couple of years back.

https://britastro.org/observations/observation.php?id=20190411_213200_531d1ec6d134b3dc

The width of the line (the doppler effect) is a measure of how fast the material near the black hole is orbiting as, if side on, we see the material  both coming towards and away from us. (Jets can also be produced coming out from the poles  which can have very high velocities)  The orbital velocity can be used to estimate the mass of the black hole.

The mass of the black hole is also closely tied to the total mass of the galaxy. In this case the two mass estimates do not agree. There is also some structure in the line ( a combination of different components moving at different velocities. You get a hint of this in my low resolution spectrum but the higher resolution spectra in the paper shows this in more detail)

The authors of the paper interpret this as an indication that there are two black holes in close orbit round each other (There are other examples of this around so we know these exist) 

What is interesting in this case is the orbital period has been dropping rapidly (from a year to month) as energy is lost from the system as gravitational waves, suggesting an imminent merger. Note though this is hot off the press and not yet a peer reviewed paper. A merger has never been observed but if it does happen though, watch this space ! As the authors put it

"Copious electromagnetic signals are expected, from radio to X-ray band, binary inspiral
stage to post merger, and from locations such as black hole corona, (possible) jet, accretion disk,
interstellar medium, etc. Neutrino production is also possibly detectable as a result of binary black
hole coalescence. We would like to call the attention of the astronomical community to perform
extensive multi-messenger, multi-band observation on this transient AGN source. Hopefully this
campaign will be celebrated by many unprecedented discoveries in the years to come."

Edited February 8, 2022 by robin_astro

[markse68]

Thanks for that very thorough explanation Robin. Fingers crossed it’s real, although i’m glad it’s not happening in our galaxy!

[PeterW]

How far away is it, what sort of brightening might a merged result in?

 

Peter

[robin_astro]

3 hours ago, PeterW said:

How far away is it, what sort of brightening might a merged result in?

The 0.081 redshift puts the galaxy at about a billion light years away. As to what we might see, nobody really knows as we have not witnessed a supermassive black hole merger before.

Cheers

Robin

Edited February 11, 2022 by robin_astro