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Astronomers investigating gamma ray emissions have discovered that certain active galaxies seem to be giving off bursts in regular patterns. This, the team says, could be an indication of galaxies harboring two supermassive black holes in their centers.

Conventional thinking says that lurking at the heart of most galaxies is a supermassive black hole. The Milky Way is the perfect example – Sagittarius A lies about 26,000 light-years from Earth and has a mass about 4 million times that of the Sun.

While it’s generally thought that galaxies would only host one supermassive black hole, the idea that some could have two has been theoretically possible. And now, an international team of researchers has found what could be the first evidence of this scenario.

A gold wedding band will melt at around 1,000 degrees Celsius and vaporize at about 2,800 degrees, but these changes are just the beginning of what can happen to matter. Crank up the temperature to trillions of degrees, and particles deep inside the atoms start to shift into new, non-atomic configurations. Physicists seek to map out these exotic states — which probably occurred during the Big Bang, and are believed to arise in neutron star collisions and powerful cosmic ray impacts — for the insight they provide into the cosmos’s most intense moments.

Now an experiment in Germany called the High Acceptance DiElectron Spectrometer (HADES) has put a new point on that map.

For decades, experimentalists have used powerful colliders to crush gold and other atoms so tightly that the elementary particles inside their protons and neutrons, called quarks, start to tug on their new neighbors or (in other cases) fly free altogether. But because these phases of so-called “quark matter” are impenetrable to most particles, researchers have studied only their aftermath. Now, though, by detecting particles emitted by the collision’s fireball itself, the HADES collaboration has gotten a more direct glimpse of the kind of quark matter thought to fill the cores of merging neutron stars.

The first evidence of an object more massive than any neutron star and more lightweight than any black hole has astronomers wondering what it is.

Every year, 2 million black hole mergers are missed — Australian scientists work out how to detect them, revealing a lost 8 billion light-years of Universe evolution.

Last year, the Advanced LIGO –VIRGO gravitational-wave detector network recorded data from 35 merging black holes and neutron stars. A great result — but what did they miss? According to Dr. Rory Smith from the ARC Centre of Excellence in Gravitational Wave Discovery at Monash University in Australia — it’s likely there are another 2 million gravitational wave events from merging black holes, “a pair of merging black holes every 200 seconds and a pair of merging neutron stars every 15 seconds” that scientists are not picking up.

Dr. Smith and his colleagues, also at Monash University, have developed a method to detect the presence of these weak or “background” events that to date have gone unnoticed, without having to detect each one individually. The method — which is currently being test driven by the LIGO community — “means that we may be able to look more than 8 billion light-years further than we are currently observing,” Dr. Smith said.

Physicists at the XENON dark matter research facility report an ‘excess’ of 53 events, which may hint at the existence of hypothetical solar axion particles. Other possibilities for the anomalous detection include a surprisingly large magnetic moment for neutrinos, and tritium contamination in the detector.

Last year, the Advanced LIGO-VIRGO gravitational-wave detector network recorded data from 35 merging black holes and neutron stars. A great result—but what did they miss? According to Dr. Rory Smith from the ARC Centre of Excellence in Gravitational Wave Discovery at Monash University in Australia—it’s likely there are another 2 million gravitational wave events from merging black holes, “a pair of merging black holes every 200 seconds and a pair of merging neutron stars every 15 seconds” that scientists are not picking up.

Dr. Smith and his colleagues, also at Monash University, have developed a method to detect the presence of these weak or “background” events that to date have gone unnoticed, without having to detect each one individually. The method—which is currently being test driven by the LIGO community—” means that we may be able to look more than 8 billion light years further than we are currently observing,” Dr. Smith said.

“This will give us a snapshot of what the early universe looked like while providing insights into the evolution of the universe.”

Scientists from the international XENON collaboration, an international experimental group including the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), University of Tokyo; the Institute for Cosmic Ray Research (ICRR), University of Tokyo; the Institute for Space-Earth Environmental Research (ISEE), Nagoya University; the Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University; and the Graduate School of Science, Kobe University, announced today that data from their XENON1T, the world’s most sensitive dark matter experiment, show a surprising excess of events. The scientists do not claim to have found dark matter. Instead, they have observed an unexpected rate of events, the source of which is not yet fully understood. The signature of the excess is similar to what might result from a tiny residual amount of tritium (a hydrogen atom with one proton and two neutrons), but could also be a sign of something more exciting—such as the existence of a new particle known as the solar axion or the indication of previously unknown properties of neutrinos.

XENON1T was operated deep underground at the INFN Laboratori Nazionali del Gran Sasso in Italy, from 2016 to 2018. It was primarily designed to detect dark matter, which makes up 85% of the matter in the universe. So far, scientists have only observed indirect evidence of dark matter, and a definitive, direct detection is yet to be made. So-called WIMPs (Weakly Interacting Massive Particles) are among the theoretically preferred candidates, and XENON1T has thus far set the best limit on their interaction probability over a wide range of WIMP masses. In addition to WIMP dark matter, XENON1T was also sensitive to different types of new particles and interactions that could explain other open questions in physics. Last year, using the same detector, these scientists published in Nature the observation of the rarest nuclear decay ever directly measured.

The XENON1T detector was filled with 3.2 tons of ultra-pure liquefied xenon, 2.0 t of which served as a target for particle interactions. When a particle crosses the target, it can generate tiny signals of light and free electrons from a xenon atom. Most of these interactions occur from particles that are known to exist. Scientists therefore carefully estimated the number of background events in XENON1T. When data of XENON1T were compared to known backgrounds, a surprising excess of 53 events over the expected 232 events was observed.

An international collaboration bringing together over 200 scientists from 13 countries has shown that the very high-energy gamma-ray emissions from quasars, galaxies with a highly energetic nucleus, are not concentrated in the region close to their central black hole, but in fact, extend over several thousand light-years along jets of plasma. This discovery shakes up current scenarios for the behavior of such plasma jets. The work, published in the journal Nature on June 18, 2020, was carried out as part of the H.E.S.S collaboration, involving in particular the CNRS and CEA in France, and the Max Planck society and a group of research institutions and universities in Germany.

Over the past few years, scientists have observed the universe using gamma rays, which are very high-energy photons. Gamma rays, among the cosmic rays that constantly bombard the Earth, originate from regions of the universe where particles are accelerated to huge energies unattainable in human-built accelerators. Gamma rays are emitted by a wide range of cosmic objects such as quasars, which are active galaxies with a highly energetic nucleus.

The intensity of the radiation emitted from these systems can vary over very short timescales of up to one minute. Scientists therefore believed that the source of this radiation was very small and located in the vicinity of a supermassive black hole, which can have a mass several billion times that of the sun’s. The black hole is thought to gobble up the matter spiraling down into it and eject a small part of it in the form of large jets of plasma at relativistic speeds, close to the speed of light, thus contributing to the redistribution of matter throughout the universe.

An excess of events spotted in the XENON1T experiment could be signs of solar axions or weird, new properties of neutrinos, but not dark matter itself.