X-ray light from the Perseus cluster of galaxies may finally reveal the true nature of one of the most mysterious substances in the cosmos: dark matter.

Dark matter is a bizarre material that does not emit light or energy, yet is thought to make up about 85 percent of the matter in the universe.

Researchers use creative and indirect observations to deduce dark matter's presence, but it remains challenging to pin down solid evidence of the substance's existence. Thanks to mounting observations by NASA's Chandra X-ray Observatory, a Japanese-led X-ray telescope known as Hitomi and the European Space Agency's (ESA) XMM-Newton, scientists may be on the verge of a groundbreaking discovery about the mysterious material, researchers said in a statement from the Chandra X-Ray Center in Cambridge, Massachusetts.

The subject of study is the Perseus cluster, a dusty region of galaxies gathered together 250 million light-years from Earth. Scientists estimate that the Perseus cluster is 11.6 million light-years across and that it may contain a whopping 660 trillion times the mass of the sun.

In 2014, an unusual spike of intensity in X-ray wavelengths caught the attention of researchers using the XMM-Newton space observatory. The waves were coming from heated gas in the Perseus galactic cluster, near the center. Researchers also found that this same wavelength of radiation, known as an emission line, was coming from 73 other galaxy clusters, according to the statement.

That 2014 observation showed radiation emanating with 3.5 kiloelectron volts (keV) of energy, and a new analysis detected an absorption of X-rays — also at 3.5 keV. 

An optical image of the Perseus cluster taken using the Hubble Space Telescope.

Surrounding a supermassive black hole at the center of the Perseus cluster. Researchers have found it nearly impossible to explain why that particular wavelength is being emitted and absorbed, and because previously-seen astronomical objects don't seem to reveal clues about the wavelength emission, they suggested dark matter could be the cause.

If dark matter caused the atypical emission and absorption lines at that wavelength — both giving off and absorbing X-rays within the collection of galaxies — further observation could teach researchers more about the mysterious substance, the scientists said.

Fortunately, powerful X-ray telescopes currently being developed will let scientists make more-precise observations of these fascinating X-ray emission lines.

Image on the top: A composite image of X-ray and optical observations of the Perseus galaxy cluster. 

This image contains X-ray data from the Chandra X-ray Observatory (blue) of the Perseus galaxy cluster. The observations have been combined with optical data from the Hubble space telescope (pink) and radio-emission data from the Very Large Array (red) in New Mexico. If these findings are confirmed with future observations, it would signal a major step forward in comprehending the nature of dark matter, researchers said in a statement.  (NASA/ESA/CXO/Oxford University/NRAO/AUI/University of Montreal)

Original article on Space.com.

An observatory in West Virginia picked up 15 bright radio pulses from a dwarf galaxy, 3 billion light years, earlier this year. The initial results, based on observations carried out by a team of astronomers and astrophysicists, postulate these pulses to have emerged from an unknown source, labeled as FRB 121102. It’s a source of fast radio bursts (FRBs).

They were first detected in 2001, and as the name suggests, FRBs are super-fast and really powerful burst of radio signals. But we still have no idea what causes them. 

"The repeating FRB source is an anomaly in the population right now; it's the only one of its kind," says Emily Petroff, a post-doctoral researcher at the Netherlands Institute for Radio Astronomy. However, Petroff was not directly involved in the current observations.  

"We're trying hard to find more (either by checking to see if other FRBs repeat, or trying to find more FRBs and monitor them)," Petroff wrote in an email. "Keep in mind that the population is still really small. Only 30 FRB sources have been found, from 29 of those we've only seen one burst, from one of them we've seen over 200!"

It's thrilling to have 15 bursts from apparently the same source, coming with a higher frequency than usual; 7 Gigahertz. Andrew Siemion, an astrophysicist and director of the Breakthrough Listen program, stated “Bursts from this source have never been seen at this high a frequency”.

Breakthrough Listen organization, funding the project, issued a press release saying “Possible explanations for FRBs range from outbursts from rotating neutron stars with extremely strong magnetic fields, to more speculative ideas that they are directed energy sources used by extraterrestrial civilizations to power spacecraft.”

It’s their job to bring up aliens as a possibility until they have something else to count on. To begin with aliens bumping in this whole scenario might seem strange but not if the news is coming from a $100 million project with its main objective to look for signals from extraterrestrial civilizations.

There are a number of other possible explanations for these repeating bursts, and most of them definitely not include aliens.

A sequence of the 15 bursts observed last weekend. Credit Siemion et al.

"With any mystery signal from space comes the inevitable question about extraterrestrial life. At the moment there's no evidence that these are encoded messages or anything like that," Petroff says. "And when dealing with a new phenomenon, the simplest explanations—such as emission from an astrophysical source (and not a spaceship)—are usually the best place to start."

It could be the last spinning remnant of a star turned supernova. These neutron stars can sometimes hurl out bright pulses into the universe, or have magnetic fields so powerful that they earn the name Magnetars. Some scientists think that FRB’s could be emitted early on in a magnetar's development.

"Most of the current theories for FRBs are centered around compact, energetic objects in other galaxies," Petroff says. "The two most compact and energetic things we know about are black holes and neutron stars; they also happen to be two of the most extreme types of objects in the universe. At the moment there are more theories than there are FRB sources, though.” Petroff further added, “The last time we had a cosmic mystery source like this was with the reporting of the discovery of gamma ray bursts in the 1970s, then it took decades to figure out what caused them and their origin.”

Continuing to observe FRBs can help get more data, and maybe eventually we’ll figure out what they are. Lots of new telescopes are coming online in the next 6 to 12 months to further probe these FRBs. The fact that we are learning more about the magnificently baffling universe is exhilarating itself.  

NASA’s Chandra X-Ray Observatory has observed very strange and distinctive X-ray signal coming from our Milky Way Galaxy that researchers believe can help them in proving the existence of the mysterious dark side of the universe. That is the claim of US scientists who analyzed the energy spectrum of X-rays.

The data was gathered by NASA’s Chandra satellite who found more X-ray photons with a particular energy than would be expected if they were generated by the decay of dark matter particles, say the researchers. This is not the first time that scientists have seen extra photons with an energy of about 3,500 electronvolts (3.5 keV) in the spectra recorded by X-ray satellites.

The researchers found that the strength of their 3.5 keV signal was consistent with data from NASA’s X-ray satellite, the Nuclear Spectroscopic Telescope Array (NuStar). With no obvious interference within the satellite itself, the researchers concluded that the signal is unlikely to be caused by instrumental noise.

"This result is very exciting," said Dr Abazajian, a cosmologist at the University of California, Irvine who was not involved in the research. "It makes it more likely that the line is due to dark matter, which makes up more than 80% of all the mass in the Universe. As its name suggests, it gives off no light, but reveals its presence through the gravitational pull it exerts on stars within galaxies.

The latest research, which targets relatively light particles of dark matter, has been carried out by Nico Cappelluti of the Yale Center for Astronomy and Astrophysics in Connecticut, US, and colleagues.

His colleague, Esra Bulbul of the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology (MIT) was the first scientist to spot an anomalous line at 3.5 keV, when looking at the X-ray spectra of large numbers of galaxy clusters in 2014. Researchers elsewhere have seen a line with the same energy in spectra from a variety of other objects, including the Andromeda and Milky Way galaxies, which are thought to be enveloped in a bubble of dark matter.

The researchers are heartened by the fact that four different satellites have now seen the same signal but are not ready to claim discovery of dark matter because, they say, it is still possible that their result is a statistical fluke - that the Chandra Observatory just happened to snare more X-rays with an energy of 3.5 keV than it did others.

"As we collect more and more X-ray data, the evidence for the 3.5 keV line is growing and growing," said Cappelluti.

Astrophysicists have been scanning the Milky Way for years for the photons generated when dark matter particles either annihilate with one another or decay. The so-called weakly-interacting massive particles (WIMPs) are believed by some researchers to be responsible for unusual emissions of gamma rays seen coming from the center of the Milky Way. While others think sources such as pulsars are probably the cause.

To establish whether dark matter could be the source, they compared Chandra's spectra to those of X-rays from the center of the Milky Way that had been detected by the European Space Agency's XMM-Newton satellite. As expected, they found the signal in the latter to be stronger, given that dark matter should be densest where there are more stars as found in the galactic center.

The researchers also ruled out a couple of alternative astrophysical sources for the signal: photons emitted either when very large black holes suck in material from their surroundings or when ions of sulphur take electrons from hydrogen in the centre of galaxy clusters. "We found that our result is consistent with previous results if you assume the cause to be dark matter," said Bulbul.

Others, however, urge caution. Dan Hooper, a particle theorist at Fermilab near Chicago, points out that a number of other studies have failed to see the line, including one by a group analysing data from the Japanese space agency's (Jaxa) ill-fated Hitomi X-ray satellite that malfunctioned just over a month after launch in February 2016, but managed to collect enough data to disprove a previously claimed sighting of the 3.5 keV line in the Perseus galaxy cluster.

"The new paper claims a modest detection," said Dr Hooper, "but it doesn't sway me very strongly at this point."

Christoph Weniger, a theoretical astroparticle physicist at the University of Amsterdam, is a little more upbeat, reorting to the BBC that the new research "adds yet another piece to the 3.5 keV puzzle".

He said that the signal might be due to a hypothetical particle known as the sterile neutrino, which would decay into an X-ray photon and a normal neutrino. But he stressed the need for more data to "confirm or reject the dark matter hypothesis".

Via DailyGalaxy

NASA's Fermi Gamma-ray Space Telescope has found a signal at the center of the neighboring Andromeda galaxy that could indicate the presence of the mysterious dark side of  the universes known as dark matter. The signal is similar to one seen by Fermi at the center of our own Milky Way galaxy.

Surprisingly, the latest Fermi data shows the gamma rays in Andromeda -- also known as M31 -- are confined to the galaxy's center instead of spread throughout. To explain this unusual distribution, scientists are proposing that the emission may come from several undetermined sources. One of them could be dark matter, an unknown substance that makes up most of the universe.

The image of the Milky Way above, shown in visible light, superimposes a gamma-ray map of the galactic center from NASA's Fermi. Raw data transitions to a view with all known sources removed, revealing a gamma-ray excess hinting at the presence of dark matter.

The Milky Way's galactic center teems with gamma-ray sources, from interacting binary systems and isolated pulsars to supernova remnants and particles colliding with interstellar gas. It's also where astronomers expect to find the galaxy's highest density of dark matter, which only affects normal matter and radiation through its gravity. Large amounts of dark matter attract normal matter, forming a foundation upon which visible structures, like galaxies, are built.

No one knows the true nature of dark matter, but WIMPs, or Weakly Interacting Massive Particles, represent a leading class of candidates. Theorists have envisioned a wide range of WIMP types, some of which may either mutually annihilate or produce an intermediate, quickly decaying particle when they collide. Both of these pathways end with the production of gamma rays -- the most energetic form of light -- at energies within the detection range of Fermi's Large Area Telescope (LAT).

When astronomers carefully subtract all known gamma-ray sources from LAT observations of the galactic center, a patch of leftover emission remains. This excess appears most prominent at energies between 1 and 3 billion electron volts (GeV) -- roughly a billion times greater than that of visible light -- and extends outward at least 5,000 light-years from the galactic center.

Hooper and his colleagues conclude that annihilations of dark matter particles with a mass between 31 and 40 GeV provide a remarkable fit for the excess based on its gamma-ray spectrum, its symmetry around the galactic center, and its overall brightness. Writing in a paper submitted to the journal Physical Review D, the researchers say that these features are difficult to reconcile with other explanations proposed so far, although they note that plausible alternatives not requiring dark matter may yet materialize.

"Dark matter in this mass range can be probed by direct detection and by the Large Hadron Collider (LHC), so if this is dark matter, we're already learning about its interactions from the lack of detection so far," said co-author Tracy Slatyer, a theoretical physicist at MIT in Cambridge, Mass. "This is a very exciting signal, and while the case is not yet closed, in the future we might well look back and say this was where we saw dark matter annihilation for the first time."

The researchers caution that it will take multiple sightings – in other astronomical objects, the LHC or in some of the direct-detection experiments now being conducted around the world -- to validate their dark matter interpretation.

A Fermi 2015 study was an example of innovative techniques applied to Fermi data by the science community, said Peter Michelson, a professor of physics at Stanford University in California and the LAT principal investigator. "The Fermi LAT Collaboration continues to examine the extraordinarily complex central region of the galaxy, but until this study is complete we can neither confirm nor refute this interesting analysis."

While the great amount of dark matter expected at the galactic center should produce a strong signal, competition from many other gamma-ray sources complicates any case for a detection. But turning the problem on its head provides another way to attack it. Instead of looking at the largest nearby collection of dark matter, look where the signal has fewer challenges.

Dwarf galaxies orbiting the Milky Way lack other types of gamma-ray emitters and contain large amounts of dark matter for their size – in fact, they're the most dark-matter-dominated sources known. But there's a tradeoff. Because they lie much farther away and contain much less total dark matter than the center of the Milky Way, dwarf galaxies produce a much weaker signal and require many years of observations to establish a secure detection.

For the past few years, the LAT team has been searching dwarf galaxies for hints of dark matter. The published results of these studies have set stringent limits on the mass ranges and interaction rates for many proposed WIMPs, even eliminating some models.

There's about a one-in-12 chance that what they saw in 2015 in the dwarf galaxies is not even a signal at all, but a fluctuation in the gamma-ray background, explained Elliott Bloom, a member of the LAT Collaboration at the Kavli Institute for Particle Astrophysics and Cosmology, jointly located at the SLAC National Accelerator Laboratory and Stanford University. If it's real, the signal should grow stronger as Fermi acquires additional years of observations and as wide-field astronomical surveys discover new dwarfs. "If we ultimately see a significant signal," he added, "it could be a very strong confirmation of the dark matter signal claimed in the galactic center."

Via NASA Goddard; A. Mellinger, CMU; T. Linden, Univ. of Chicago