Repeating outflows of hot wind found close to black hole

Repeating outflows of hot wind found close to black hole
Credit: John Paice/University of Southampton/Inter-University Centre for Astronomy

An international team of astrophysicists from Southampton, Oxford and South Africa have detected a very hot, dense outflowing wind close to a black hole at least 25,000 light-years from Earth.

Lead researcher Professor Phil Charles from the University of Southampton explained that the gas (ionised helium and hydrogen) was emitted in bursts which repeated every 8 minutes, the first time this behaviour has been seen around a black hole. The findings have been published in the journal Monthly Notices of the Royal Astronomical Society.

The object Professor Charles's team studied was Swift J1357.2-0933 which was first discovered as an X-ray transient—a system that exhibits violent outbursts—in 2011. These transients all consist of a low-mass star, similar to our Sun and a compact object, which can be a white dwarf, neutron star or black hole. In this case, Swift J1357.2-0933 has a black hole compact object which is at least 6 times the mass of our Sun.

Material from the normal star is pulled by the compact object into a disc in between the two. Massive outbursts occur when the material in the disc becomes hot and unstable and it releases copious amounts of energy.

Professor Charles said: "What was particularly unusual about this system was that ground-based telescopes had revealed that its optical brightness displayed periodic dips in its output and that the period of these dips slowly changed from around two minutes to about 10 minutes as the outburst evolved. Such strange behaviour has never been seen in any other object.

"The cause of these remarkable, fast dips has been a hot topic of scientific debate ever since their discovery. So it was with great excitement that astronomers greeted the second outburst of this object in mid-2017, presenting an opportunity to study this strange behaviour in greater detail."

Professor Charles and his team recognised that key to getting the answer was to obtain optical spectra a number of times during each dip cycle, essentially studying how their colour changed with time. But with the object about 10,000 times fainter than the faintest star visible to the naked eye and the dip period of only around 8 minutes, a very big telescope had to be used.

So, they used SALT, the Southern African Large Telescope, the largest optical telescope in the southern hemisphere.

The University of Southampton is one of the founding UK partners in SALT, and together with their South African collaborators, are part of a multi-partner Large Science Programme to study transients of all types. Not only does SALT have the necessary huge collecting area (it has a 10m diameter mirror), but it is operated in a 100 percent queue-scheduled way by resident staff astronomers, meaning that it can readily respond to unpredictable transient events. This was perfect for Swift J1357.2-0933, and SALT obtained more than an hour of spectra, with one taken every 100 seconds.

"Our timely observations of this fascinating system demonstrates how the quick response of SALT, through its flexible queue-scheduled operation, makes it an ideal facility for follow-up studies of transient objects," said Dr. David Buckley, the Principal Investigator of the SALT transient programme, based at the South African Astronomical Observatory, who also added, "With the instantaneous availability of a number of different instruments on SALT, we can also dynamically modify our observing plans to suit the science goals and react to results, almost in real-time"

Professor Charles added: "The results from these spectra were stunning. They showed ionised helium in absorption, which had never been seen in such systems before. This indicated that it must be both dense and hot—around 40,000 degrees. More remarkably, the spectral features were blue-shifted (due to the Doppler effect), indicating that they were blowing towards us at about 600km/s. But what really astonished us was the discovery that these spectral features were visible only during the optical dips in the light-curve. We have interpreted this quite unique property as due to a warp or ripple in the inner accretion disc that orbits the black hole on the dipping timescale. This warp is very close to the black hole at just one tenth the radius of the disc."

What is driving this matter away from the black hole? It is almost certainly the radiation pressure of the intense X-rays generated close to the black hole. But it has to be much brighter than we see directly, suggesting that the material falling on to the black hole obscures it from direct view, like clouds obscuring the Sun. This occurs because we happen to be viewing the binary system from a vantage point where the disc appears edge-on, as depicted in the schematic illustration, and rotating blobs in this disc obscure our view of the central black hole.

Interestingly there are no eclipses by the companion star seen in either the optical or X-ray as might be expected. This is explained by it being very small, and constantly in the shadow of the disc. This inference comes from detailed theoretical modelling of winds being blown off accretion discs that was undertaken by one of the team, James Matthews at the University of Oxford, using supercomputer calculations.

This object has remarkable properties amongst an already interesting group of objects that have much to teach us about the end-points of stellar evolution and the formation of compact objects. We already know of a couple of dozen black hole binary systems in our Galaxy, which all have masses in the 5-15 solar mass range, and the single black hole at our Galactic Centre is around 4 million solar masses. They all grow by the accretion of matter that we have witnessed so spectacularly in this object. We also know that a substantial fraction of the accreting material is being blown away. When that happens from the supermassive at the centres of galaxies, those powerful winds and jets can have a huge impact on the rest of the galaxy.

Professor Charles concluded: "These short-period binary versions are a perfect way to study this physics in action."

Explore further

Hubble discovers mysterious black hole disc

More information: Hot, dense HeII outflows during the 2017 outburst of the X-ray transient Swift J1357.2-0933 Monthly Notices of the Royal Astronomical Society: Letters, slz120,
Citation: Repeating outflows of hot wind found close to black hole (2019, August 6) retrieved 14 October 2019 from
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Aug 06, 2019
Expanding galaxys born inside to outside.

Also expanding black stars emit expanding light, but black stars expanding light is dark for us.

Aug 06, 2019
You dont understund that Nucleus of atoms expanding and recycling dark expanding pushing force which have example nature of expanding light.

Expanding light waves is dark for us, but we know, there is waves because we can register photons.

But almost all expanding light mass is in dark expanding waves.

Expanding lights interactive with eachother and get eachother expanding faster and faster. So expanding light moving faster and faster same way what matter and light expanding.

Aug 06, 2019
This comment has been removed by a moderator.

Aug 06, 2019

No, no and no.

Aug 06, 2019

No, no and no.

LOL, I see that SpookyOtto's sock puppy was able to spoof the article in his first 3 comments above. What a shame that the first 3 spaces of bandwidth was taken up by silly nonsensical dog-poop. Otto loves spoofing articles while also trolling commentators such as hat1208 the gullible.

Aug 06, 2019
After clicking on the link, the returned message was "DOI not found".

Aug 06, 2019
After clicking on the link, the returned message was "DOI not found".

Had the same problem. After digging I found this: https://academic....z120.pdf

Aug 06, 2019
Outflows are ubiquitous in astrophysics. Despite different sizes, velocity and amount of transported energy, luminosity and degree of collimation, they have obvious morphological similarities. However, what is important for us, there is the picture of the outflows from everywhere and none of inflows into somewhere. That is an obvious asymmetry.

Aug 06, 2019
Nice, @Circles, Thanks.

Aug 07, 2019
"outflows" are nothing more than the exact same phenomena as when you are taking a whiz into your toilet
resulting in some of the bowl water & piss splattering up onto your legs

just simple applications of Newtonian Physics
"For every action..."

more proof that the BH's accretion disks are as exciting as demolition derby, fueled with nitrous oxide
(hey, it makes me laugh!)

the editor who penned this clickbait headline?
back about the 70's or 80's was flunking Basic Physics
so he transferred to English Lit for his major

now that he's got your eyeballs firmly pinned to these pages?
make sure you check out several of the advertisers
they are the ones funding this forum

Aug 07, 2019
Expanding space and curving space is naked empire.

Space dont emit information.

You cant proof science way that there is expanding space or curving space.

We can check out if light expanding and interactive with eachother. I dont mean that photons interactive with eachother.

I mean that expanding light have dark expanding waves which interactive with eachother. Photons moving with dark waves.

So, we can try manipulate photons moving direction with billion years old light which have pushing force which can change photons moving direction.

We post to go to space and make very long trough / wall and other end we need telescope.

Then we just look faraway galaxy place which we already know. Then you can see it look to be different place because billions years old expanding light can push photons from faraway galaxy.

How you can try manipulate space?

You cant.

So, you can only believe there is expanding space and curving space.

Aug 07, 2019

No. [I did not read, I have you blocked, but I'm sure hat1208 has diagnosed your comments correctly. :-)]

Aug 07, 2019
well mrpushmepullme
it must be very difficult for you when the caretaker turns off the lights?
& a solid body of darkness envelops you like a fly in aspic

care to show your defining mathematics of your fantasy of solid dark?

by the wayside, how does starlight get through dark as a solid object?

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