A source accelerating Galactic cosmic rays to unprecedented energy discovered at the centre of the Milky Way

March 16, 2016
Artist's impression of the giant molecular clouds surrounding the Galactic Centre, bombarded by very high energy protons accelerated in the vicinity of the central black hole and subsequently shining in gamma rays. Credit: © Dr Mark A. Garlick/ H.E.S.S. Collaboration

For more than 10 years the H.E.S.S. observatory in Namibia, run by an international collaboration of 42 institutions in 12 countries, has been mapping the center of our galaxy in very-high-energy gamma rays. These gamma rays are produced by cosmic rays from the innermost region of the galaxy. A detailed analysis of the latest H.E.S.S. data, published on 16 March 2016 in Nature, reveals for the first time a source of this cosmic radiation at energies never observed before in the Milky Way: the supermassive black hole at the center of the galaxy, likely to accelerate cosmic rays to energies 100 times larger than those achieved at the largest terrestrial particle accelerator, the LHC at CERN.

The Earth is constantly bombarded by high-energy particles (protons, electrons and atomic nuclei) of , particles that comprise the so-called "." These "cosmic rays" are electrically charged, and are hence strongly deflected by the interstellar magnetic fields that pervade our galaxy. Their path through the cosmos is randomized by these deflections, making it impossible to directly identify the astrophysical sources responsible for their production. Thus, for more than a century, the origin of the cosmic rays remains one of the most enduring mysteries of science.

Fortunately, cosmic rays interact with light and gas in the neighborhood of their sources, producing gamma rays. These gamma rays travel in straight lines, undeflected by magnetic fields, and can therefore be traced back to their origin. When a very-high-energy gamma ray reaches the Earth, it interacts with a molecule in the upper atmosphere, producing a shower of secondary particles that emit a short pulse of "Cherenkov light." By detecting these flashes of light using telescopes equipped with large mirrors, sensitive photo-detectors, and fast electronics, more than 100 sources of very-high-energy gamma rays have been identified over the past three decades. The H.E.S.S. (High Energy Stereoscopic System) observatory in Namibia represents the latest generation of such telescope arrays. It is operated by scientists from 42 institutions in 12 countries, with major contributions by MPIK Heidelberg, Germany, CEA and CNRS, France.

A source accelerating Galactic cosmic rays to unprecedented energy discovered at the centre of the Milky Way
Artist's impression of the giant molecular clouds surrounding the Galactic Centre, bombarded by very high energy protons accelerated in the vicinity of the central black hole and subsequently shining in gamma rays. Credit: © Dr Mark A. Garlick/ H.E.S.S. Collaboration

Today we know that cosmic rays with energies up to approximately 100 teraelectronvolts (TeV) are produced in our galaxy, by objects such as supernova remnants and pulsar wind nebulae. Theoretical arguments and direct measurements of cosmic rays reaching the Earth indicate, however, that the cosmic-ray factories in our galaxy should be able to provide particles up to one petaelectronvolt (PeV) at least. While many multi-TeV accelerators have been discovered in recent years, the search for the sources of the highest energy has, so far, been unsuccessful.

Detailed observations of the galactic center region, made by H.E.S.S. over the past 10 years, and published today in the journal Nature, finally provide direct indications for such PeV cosmic-ray acceleration. During the first three years of observations, H.E.S.S. uncovered a very powerful point source of gamma rays in the galactic-center region, as well as diffuse gamma-ray emission from the giant molecular clouds that surround it in a region approximately 500 light-years across. These molecular clouds are bombarded by cosmic rays moving at close to the speed of light, which produce gamma rays through their interactions with the matter in the clouds. A remarkably good spatial coincidence between the observed and the density of material in the clouds indicated the presence of one or more accelerators of cosmic rays in that region. However, the nature of the source remained a mystery.

Deeper observations obtained by H.E.S.S. between 2004 and 2013 shed new light on the processes powering the cosmic rays in this region. According to Aion Viana (MPIK, Heidelberg), "the unprecedented amount of data and progress made in analysis methodologies enables us to measure simultaneously the spatial distribution and the energy of the cosmic rays." With these unique measurements, H.E.S.S. scientists are for the first time able to pinpoint the source of these particles: "Somewhere within the central 33 light-years of the Milky Way there is an astrophysical source capable of accelerating protons to energies of about one petaelectronvolt, continuously for at least 1,000 years," says Emmanuel Moulin (CEA, Saclay). In analogy to the "Tevatron," the first human-built accelerator that reached energies of 1 TeV, this new class of cosmic accelerator has been dubbed a "Pevatron." "With H.E.S.S. we are now able to trace the propagation of PeV protons in the central region of the galaxy," adds Stefano Gabici (CNRS, Paris).

The center of our galaxy is home to many objects capable of producing cosmic rays of high energy, including, in particular, a supernova remnant, a pulsar wind nebula, and a compact cluster of massive stars. However, "the located at the center of the galaxy, called Sgr A*, is the most plausible source of the PeV protons," says Felix Aharonian (MPIK, Heidelberg and DIAS, Dublin), adding that, "several possible acceleration regions can be considered, either in the immediate vicinity of the black hole, or further away, where a fraction of the material falling into the black hole is ejected back into the environment, thereby initiating the acceleration of particles."

The H.E.S.S. measurement of the gamma-ray emission can be used to infer the spectrum of the protons that have been accelerated by the central black hole—revealing that Sgr A* is very likely accelerating protons to PeV energies. Currently, these protons cannot account for the total flux of cosmic rays detected at the Earth. "If, however, our central black hole was more active in the past," the scientists argue, "then it could indeed be responsible for the bulk of the galactic that are observed today at the Earth." If true, this would dramatically influence the century old debate concerning the origin of these enigmatic particles.

Explore further: New clues in the hunt for the sources of cosmic neutrinos

More information: A. Abramowski et al. Acceleration of petaelectronvolt protons in the Galactic Centre, Nature (2016). DOI: 10.1038/nature17147

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vlaaing peerd
5 / 5 (5) Mar 17, 2016
erhm, if the LHC is accelarating particles to up to 99,9~% the speed of light, how is this supposed to be 100x faster?

Edit: never mind, it was 100x more energy, not speed.
cantdrive85
1.7 / 5 (11) Mar 17, 2016
Of course, there exist no mechanism of gravity that can legitimately explain the acceleration of charged particles to these energies. Blaming this real phenomena on a fictional mathematical entity such as a BH is both ingenuous and remarkably lazy. Only powerful electric fields can produce the observed phenomena, to suggest the weakest force in nature (gravity) is capable of doing these things just highlights the extreme ignorance pervading astrophysics.
HannesAlfven
1.6 / 5 (7) Mar 17, 2016
Double layers should be classified as celestial objects. The Van Allen probes observed 7,000 of them in just a few minutes while traveling through our own local belts. Double layers have been studied in the plasma laboratory for many decades now, confirming that they can accelerate charged particles. MHD models cannot accommodate double layers. The solution is not to get rid of double layers; it's to scale back the application of MHD to astrophysical phenomena. There have been people arguing for this since the inception of the popularity of MHD.
Tuxford
1 / 5 (7) Mar 17, 2016
Cosmic ray accerelation from Sag. A?? This is direct evidence of LaViolette's long-standing Superwave theory, where cosmic rays are periodically ejected for extended periods at elevated levels that can dramatically change our own climate. The last major passing superwave dates back to the ice age, where LaViolette has now published evidence of such found in the ice core record.
Captain Stumpy
4.1 / 5 (9) Mar 17, 2016
Only powerful electric fields can produce the observed phenomena
@cd
yeah? you mean like how the electric plasma invisible unicorn of AAaaaaaaargh broke up Shoemaker-Levy 9?

.

.

@hannes
not even going to get into the MHD argument until you can actually give evidence of the failure of modern MHD models... especially considering it is the EE's and plasma physics specialists using it in places like PPPL.gov along side of astrophysicists to give evidence for astro's

maybe you can use this... try it. you may learn something
http://ocw.mit.ed...ophysics
Tuxford
1.2 / 5 (9) Mar 17, 2016
Currently, these protons cannot account for the total flux of cosmic rays detected at the Earth. "If, however, our central black hole was more active in the past," the scientists argue, "then it could indeed be responsible for the bulk of the galactic cosmic rays that are observed today at the Earth."


In LaViolette's model, cosmic ray super waves emanating from the supermassive grey core star are intermittent for a core of this size. And when in the especially active state, life on Earth might become problematic, forcing humans into caves, or worse. Perhaps even the dinosaur extinction events were caused by a massive eruption of cosmic rays from the core?
Enthusiastic Fool
4.2 / 5 (5) Mar 18, 2016
supermassive grey core star


Inquiring minds want to know: What would the radius of the Milky Way's "core star" be? and why is it less than 44 million km?
Azrael
4.3 / 5 (8) Mar 18, 2016
Of course, there exist no mechanism of gravity that can legitimately explain the acceleration of charged particles to these energies. Blaming this real phenomena on a fictional mathematical entity such as a BH is both ingenuous and remarkably lazy. Only powerful electric fields can produce the observed phenomena, to suggest the weakest force in nature (gravity) is capable of doing these things just highlights the extreme ignorance pervading astrophysics.


It's not the gravity of a black hole that accelerates the charged particles... It's the incredible magnetic field around some or all black holes, which if I understand correctly, are generated by in-falling super-heated matter in an accretion disk or otherwise.
cantdrive85
1.7 / 5 (6) Mar 19, 2016
Of course, there exist no mechanism of gravity that can legitimately explain the acceleration of charged particles to these energies. Blaming this real phenomena on a fictional mathematical entity such as a BH is both ingenuous and remarkably lazy. Only powerful electric fields can produce the observed phenomena, to suggest the weakest force in nature (gravity) is capable of doing these things just highlights the extreme ignorance pervading astrophysics.


It's not the gravity of a black hole that accelerates the charged particles... It's the incredible magnetic field around some or all black holes, which if I understand correctly, are generated by in-falling super-heated matter in an accretion disk or otherwise.

Being that BH's are little more than fanciful imaginings of mathematical pseudoscientists there is no possibility of your nonsensical claims. But if you want to believe in unicorns and leprechauns, so be it.
vidyunmaya
1.6 / 5 (7) Mar 19, 2016
Plasma Regulated electromagnetic phenomena in magnetic Field environment
search heart of the Universe and projections sent to ESA proposals-2010
see Books at lulu.Questions arise- searching Minds-Guiding Spirit
15 books at www[dot]lulu [dot]com-spotlight-jnani108
necessity-demand- save Earth planet from unwanted Energies-through LHC that mislead spirit of science advancement
kochevnik
5 / 5 (3) Mar 19, 2016
Being that BH's are little more than fanciful imaginings of mathematical...
Technically you are correct, as BHs fall outside spacetime. Indeed they are though to be inverted, with three dimensions of time and one of space making timespace. They don't exist within THIS spacetime, though their event horizon is noteworthy
FineStructureConstant
4.7 / 5 (10) Mar 20, 2016
Oh. My. God(TM) - so many nutcases here, they're like a swarm of wasps attracted to something sweet and, like wasps, they achieve precisely nothing. Except annoying buzzing and stinging, and making more wasps...

Meanwhile, back in the land of sanity and rigorous scientific method, good results like those in this article continue to add to our growing body of knowledge and understanding of the universe.
FineStructureConstant
4.6 / 5 (10) Mar 20, 2016
But if you want to believe in unicorns and leprechauns, so be it.
Oh, that's good, coming from a fully paid-up member of the Electric Unicorn "organization": if one could imagine a bunch of demented sheep as being organized...
Protoplasmix
5 / 5 (6) Mar 20, 2016
Being that BH's are little more than fanciful imaginings of mathematical pseudoscientists there is no possibility of your nonsensical claims. But if you want to believe in unicorns and leprechauns, so be it.
Time has told, cantdrive, and it will continue to tell, and you will likely continue trying to say otherwise.
HannesAlfven
1 / 5 (4) Mar 21, 2016
Re: "not even going to get into the MHD argument until you can actually give evidence of the failure of modern MHD models... especially considering it is the EE's and plasma physics specialists using it in places like PPPL.gov along side of astrophysicists to give evidence for astro's"

You lend the impression to those who have yet to look into it that this is complicated. It's not.

A fluid with a frozen-in magnetic field (MHD version) commonly diverges from the behavior of an electrodynamic plasma (what we observe in the laboratory).

MHD models the plasma as lacking any ability to create and maintain an E-field. This logic assumes that there are no double layers, which are known to violate MHD. Yet, the Van Allen probes have already shown that double layers can be quite common in space. And numerous papers were already published proposing that double layers exist in the ionosphere as well.
cantdrive85
1 / 5 (4) Mar 21, 2016
MHD models the plasma as lacking any ability to create and maintain an E-field. This logic assumes that there are no double layers, which are known to violate MHD. Yet, the Van Allen probes have already shown that double layers can be quite common in space.

What most folks don't understand is this one measurement confirming the existence of DL's pretty much falsified most of "modern" astrophysics guesses and the relevant "science" based upon those guesses. Nearly all stellar guesses? Bunk! Space energy transmission (i.e., AGWism)? Total bunk! Planetary formation? Completely useless! All guesses based on MHD? Utter garbage. BH and BB "theories" are nothing more than nonsensical BS. To sum up, nearly all of astrophysics is little more than pseudoscience with a twist of metaphysics. Religious followers of the Church of Scientism will argue til blue in the face, but what else would you expect from acolytes?
Phys1
5 / 5 (4) Mar 21, 2016
Being that BH's are little more than fanciful imaginings of mathematical...
Technically you are correct, as BHs fall outside spacetime. Indeed they are though to be inverted, with three dimensions of time and one of space making timespace. They don't exist within THIS spacetime, though their event horizon is noteworthy

I protest. He is correct by coincidence, like a broken clock twice a day.
Da Schneib
5 / 5 (3) Mar 21, 2016
Good stuff. It's been a curiosity where these extremely energetic cosmic rays have been coming from. It is, however, not entirely comforting that Sgr A* has been much more active than it is now recently enough that there are still some around from that period; it indicates that its activity could increase again.

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