Herschel finds hot gas on menu for Milky Way's black hole

May 07, 2013
The environment at the centre of our Milky Way Galaxy. The Galactic Centre hosts a supermassive black hole in the region known as Sagittarius A*, or Sgr A*, with a mass of about four million times that of our Sun. A dense torus of molecular gas and dust surrounds the Galactic Centre and occupies the innermost 15 light-years of our Galaxy. Enshrouded within the disc is a central cavity, with a radius of a few light-years, filled with warm dust and lower density gas.Part of this gas is being heated by the strong ultraviolet radiation from massive stars that closely orbit the central black hole. Heating also likely results from strong shocks, generated as gas orbits around or flows towards Sgr A*, in collisions between gas clouds or in material flowing at high velocity from stars and protostars. Credits: ESA–C. Carreau

(Phys.org) —ESA's Herschel space observatory has made detailed observations of surprisingly hot molecular gas that may be orbiting or falling towards the supermassive black hole lurking at the center of our Milky Way galaxy.

Our local black hole is located in a region known as Sagittarius A*—Sgr A*—after a nearby radio source. It has a mass about four million times that of our Sun and lies around 26,000 light-years away from the solar system.

Even at that distance, it is a few hundred times closer to us than any other galaxy with an active black hole at its center, making it the ideal natural laboratory to study the environment around these enigmatic objects.

Vast amounts of dust lie in the plane of the Milky Way between here and its center, obscuring our view at . But at far-, it is possible to peer through the dust, affording Herschel's scientists the chance to study the turbulent innermost region of our galaxy in great detail.

Herschel has detected a great variety of simple molecules at the Milky Way's heart, including carbon monoxide, and hydrogen cyanide. By analyzing the signature from these molecules, astronomers have been able to probe some of the of the surrounding the black hole.

"Herschel has resolved the far- within just 1 light-year of the black hole, making it possible for the first time at these wavelengths to separate emission due to the central cavity from that of the surrounding dense molecular disc," says Javier Goicoechea of the Centro de Astrobiología, Spain, and lead author of the paper reporting the results.

The biggest surprise was quite how hot the molecular gas in the innermost central region of the galaxy gets. At least some of it is around 1,000°C, much hotter than typical , which are usually only a few tens of degrees above the -273°C of absolute zero.

This illustration combines a view obtained at radio wavelengths of ionised gas at the centre of our Galaxy, the Milky Way (left panel), with a spectrum towards the very centre taken with ESA's Herschel at far-infrared wavelengths (right panel). The spectrum shows the rich variety of molecules that have been detected in this region, which range from carbon monoxide and water vapour to hydrogen cyanide and many light molecules that play a critical role in the chemistry of the interstellar medium. Some of them have been detected for the first time with Herschel. These data show that the molecular gas is surprisingly hot – the temperature estimated from the emission from carbon monoxide reaches up to 1000 ºC. The most likely source of heating of the hot molecular gas are shocks that develop as gas orbits around or flows towards Sagittarius A*, the region hosting the supermassive black hole that lies at the centre of the Milky Way. Copyright Radio-wavelength image: National Radio Astronomy Observatory/Very Large Array (courtesy of C. Lang); spectrum: ESA/Herschel/PACS & SPIRE/J.R. Goicoechea et al. (2013).

While some of the heating is down to the fierce ultraviolet radiation pouring from a cluster of massive stars that live very close to the galactic center, they are not enough to explain the high temperatures alone.

In addition to the stellar radiation, Dr. Goicoechea's team hypothesize that emission from strong shocks in highly-magnetized gas in the region may be a significant contributor to the high temperatures. Such shocks can be generated in collisions between gas clouds, or in material flowing at high speed from stars and protostars.

"The observations are also consistent with streamers of hot gas speeding towards Sgr A*, falling towards the very center of the galaxy," says Dr. Goicoechea. "Our galaxy's black hole may be cooking its dinner right in front of Herschel's eyes."

Just before material falls into a black hole, it is heated up enormously and can cause high-energy X-ray and gamma-ray flares. While Sgr A* currently shows little sign of such activity, this could change soon.

Using near-infrared observations, other astronomers have spotted a separate, compact cloud of gas amounting to just a few Earth masses spiraling towards the black hole. Located much closer to the black hole than the reservoir of material studied by Herschel in this work, it may finally be gobbled up later this year.

Spacecraft including ESA's XMM-Newton and Integral will be waiting to spot any high-energy burps as the black hole enjoys its feast.

"The center of the Milky Way is a complex region, but with these Herschel observations, we have taken an important step forward in our understanding of the vicinity of a , which will ultimately help improve our picture of galaxy evolution," says Göran Pilbratt, ESA's project scientist.

Explore further: The riddle of galactic thin–thick disk solved

More information: "Herschel Far-Infrared Spectroscopy of the Galactic Center. Hot Molecular Gas: Shocks versus Radiation near Sgr A*" by J. R. Goicoechea et al. is accepted for publication in Astrophysical Journal Letters, 7 May 2013; preprint: arxiv.org/abs/1305.1119

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May 07, 2013
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1 / 5 (4) May 07, 2013
*The observations are also consistent with Sgr A being somewhat gray, rather than black. *

See how easy such statements are to make. Just say it with authority, and the masses will follow. People crave explanations, regardless of their validity.
5 / 5 (7) May 07, 2013
you cannot apply gas laws to plasma

It's a mix of gas, plasma, liquid and solid materials. When they say 1000 C, that's just an average. You MUST take the gas laws into account, as well as ALL the other rules that apply here. This isn't a laboratory plasma experiment. There's all kinds of stuff mixed in these clouds. We've been over this before, but you refuse to learn anything.
1 / 5 (4) May 07, 2013
When "all of that mixed up stuff" is immersed in plasma, it behaves as if it's plasma. It's you who refuses to learn anything, the papers are all there but you ignore them in favor of your pet theory devised before it was known the Universe is pervaded by plasma.


1 / 5 (2) May 07, 2013
It's interesting that people will take one of the most energetic objects we know of in the universe and still apply a mechanistic worldview to it. Clouds are fluffy, usually white things which harmlessly & happily hover above our heads. By contrast, the material observed near this "black hole" is a "compact cloud of gas ... spiraling towards the black hole". It's not really clear what features of these observations justify the mechanistic phenomena which are invoked to explain it ...

"emission from strong shocks in highly-magnetized gas ... generated in collisions between gas clouds, or in material flowing at high speed from stars and protostars."

In reverse, we can ask: What does any of this behavior have to do with the clouds which we are familiar with?

And upon further inspection of Gerrit Verschuur's work, we see that "Neutral hydrogen (HI) surveys at high galactic latitudes show that the interstellar gas is filamentary".

So, why do we continue to use the word, "clouds"?
5 / 5 (1) May 07, 2013
So, why do we continue to use the word, "clouds"?

It seems the closest that would be familiar to laymen or do you have a better suggestion?
1 / 5 (2) May 07, 2013
So, why do we continue to use the word, "clouds"?

It seems the closest that would be familiar to laymen or do you have a better suggestion?

Since when does the scientific community name things based upon the laymen? I guess A. Alda was just blathering about jargon recently.
1 / 5 (2) May 08, 2013
When "all of that mixed up stuff" is immersed in plasma, it behaves as if it's plasma.

You are over-esitmating the ratio of plasma to non-plasma, as usual. The spectral diagram shows neutral oxygen, carbon, and water vapor. Solid material won't show up in this kind of observation, but observations of similar gas clouds in other wavelengths shows that solid material is typical of these clouds. Tell me why solids would act like plasma? As a matter of fact, why would neutral gas act like plasma? Highly active plasma floating freely in space isn't stable. It would seek to equalize its own distribution of energy and disperse if not for the laws of gravity and gas pressure. It's not magical.
2 / 5 (2) May 08, 2013
And upon further inspection of Gerrit Verschuur's work, we see that "Neutral hydrogen (HI) surveys at high galactic latitudes show that the interstellar gas is filamentary".

So, why do we continue to use the word, "clouds"?

Semantics. Call it a pickel if you like. We use the word cloud because everyone knows what you mean when you say cloud. The word filamentary is a descriptor which tells what kind of cloud it is. You can't just call the gas here a filament, because there are many types of filament. For example, you can have a filament of concrete or a filament of cloth. Relax and accept the common language used for casual discussions. This isn't a doctoral thesis, it's a news summary.
1.5 / 5 (6) May 08, 2013
Highly active plasma floating freely in space isn't stable. It would seek to equalize its own distribution of energy and disperse if not for the laws of gravity and gas pressure.

Gravity and gas pressure have almost ZERO effect upon plasma compared to EM, but that won't stop astrofizzlcisits from applying laws where they don't apply. How can a solid behave as a plasma? Well obviously you didn't read the very article to which I referred, they explain clearly how the dust (solid) behaves as a plasma. Why don't you direct me to even one paper that supports what you claim with REAL laboratory results, not just hypothetical theoretical models or inferences based upon assumptions. I'm not holding my breath, astrofizzlcists tend to rely upon nothing more than mental masturbation and misapplication of known laws.
1 / 5 (4) May 08, 2013
I would also like to point out that when a particular "science" cannot be tested through experimentation to verify predictions and observations it is not science, it's metaphysics. Ironically, much of the "standard theory" and GR especially do not meet with these qualifications to be considered science. They are merely exercises of philosophical metaphysics. As Tesla so succinctly pointed out in regards to GR;
"...magnificent mathematical garb which fascinates, dazzles and makes people blind to the underlying errors. The theory is like a beggar clothed in purple whom ignorant people take for a king ... its exponents are brilliant men but they are metaphysicists, not scientists..." New York Times, July 11, 1935, p23, c8

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