Here is a new report from ESO (European Southern Observatory):

Spinning Black Hole Swallowing Star Explains Superluminous Event
ESO telescopes help reinterpret brilliant explosion 

An extraordinarily brilliant point of light seen in a distant galaxy, and dubbed ASASSN-15lh, was thought to be the brightest supernova ever seen. But new observations from several observatories, including ESO, have now cast doubt on this classification. Instead, a group of astronomers propose that the source was an even more extreme and very rare event — a rapidly spinning black hole ripping apart a passing star that came too close.

This animation shows how the ASASSN-15lh most likely happened. A Sun-like star gets into the area of influence of a rapidly spinning supermassive black hole in the centre of a distant galaxy. While its orbit gets constantly closer to the black hole the star gets “spaghettified”, creating an accretion disc around the supermassive black hole. When it finally gets ripped apart close to the event horizon it creates a bright flash, that could resemble a superluminous supernova. Credit: ESO, ESA/Hubble, M. Kornmesser

An international team, led by Giorgos Leloudas at the Weizmann Institute of Science, Israel, and the Dark Cosmology Centre, Denmark, has now made additional observations of the distant galaxy, about 4 billion light-years from Earth, where the explosion took place and they have proposed a new explanation for this extraordinary event.

“We observed the source for 10 months following the event and have concluded that the explanation is unlikely to lie with an extraordinarily bright supernova. Our results indicate that the event was probably caused by a rapidly spinning supermassive black hole as it destroyed a low-mass star,”

explains Leloudas.

In this scenario, the extreme gravitational forces of a supermassive black hole, located in the centre of the host galaxy, ripped apart a Sun-like star that wandered too close — a so-called tidal disruption event, something so far only observed about 10 times. In the process, the star was “spaghettified” and shocks in the colliding debris as well as heat generated in accretion led to a burst of light. This gave the event the appearance of a very bright supernova explosion, even though the star would not have become a supernova on its own as it did not have enough mass.

“There are several independent aspects to the observations that suggest that this event was indeed a tidal disruption and not a superluminous supernova,”

explains coauthor Morgan Fraser from the University of Cambridge, UK (now at University College Dublin, Ireland).

This simulation shows a star getting torn apart by the gravitational tides of a supermassive black hole. The star gets “spaghettified” and after several orbits creates an accretion disc. Scientists believe that the superluminous ASASSN-15lh event originated in this way. The view on the right is from the side and that at the left face on. Credit: ESO, ESA/Hubble, N. Stone, K. Hayasaki

In particular, the data revealed that the event went through three distinct phases over the 10 months of follow-up observations. These data overall more closely resemble what is expected for a tidal disruption than a superluminous supernova. An observed re-brightening in ultraviolet light as well as a temperature increase further reduce the likelihood of a supernova event. Furthermore, the location of the event — a red, massive and passive galaxy — is not the usual home for a superluminous supernova explosion, which normally occur in blue, star-forming dwarf galaxies.

Although the team say a supernova source is therefore very unlikely, they accept that a classical tidal disruption event would not be an adequate explanation for the event either. Team member Nicholas Stone from Columbia University, USA, elaborates:

“The tidal disruption event we propose cannot be explained with a non-spinning supermassive black hole. We argue that ASASSN-15lh was a tidal disruption event arising from a very particular kind of black hole.”

The mass of the host galaxy implies that the supermassive black hole at its centre has a mass of at least 100 million times that of the Sun. A black hole of this mass would normally be unable to disrupt stars outside of its event horizon — the boundary within which nothing is able to escape its gravitational pull. However, if the black hole is a particular kind that happens to be rapidly spinning — a so-called Kerr black hole — the situation changes and this limit no longer applies.

“Even with all the collected data we cannot say with 100% certainty that the ASASSN-15lh event was a tidal disruption event,” concludes Leloudas. “But it is by far the most likely explanation.”

Notes

[1] As well as the data from ESO’s Very Large Telescope, the New Technology Telescope and the NASA/ESA Hubble Space Telescope the team used observations from NASA’s Swift telescope, the Las Cumbres Observatory Global Telescope (LCOGT), the Australia Telescope Compact Array, ESA’s XMM-Newton, the Wide-Field Spectrograph (WiFeS)and the Magellan Telescope.

The latest report from the ESO (European Southern Observatory):

Dark Matter May be Smoother than Expected
Careful study of large area of sky imaged by VST reveals intriguing result

Analysis of a giant new galaxy survey, made with ESO’s VLT Survey Telescope in Chile, suggests that dark matter may be less dense and more smoothly distributed throughout space than previously thought. An international team used data from the Kilo Degree Survey (KiDS) to study how the light from about 15 million distant galaxies was affected by the gravitational influence of matter on the largest scales in the Universe. The results appear to be in disagreement with earlier results from the Planck satellite.

By exploiting the exquisite image quality available to the VST at the Paranal site, and using innovative computer software, the team were able to carry out one of the most precise measurements ever made of an effect known as cosmic shear. This is a subtle variant of weak gravitational lensing, in which the light emitted from distant galaxies is slightly warped by the gravitational effect of large amounts of matter, such as galaxy clusters.

This video shows the location of one of the five KiDS regions that were surveyed by the VLT Survey Telescope at ESO’s Paranal Observatory in Chile. This region (known as G12) covers a large area of sky along the celestial equator in the constellations of Leo (The Lion) and Virgo (The Virgin). The final colour dark matter density image reveals an expansive web of dense (light) and empty (dark) regions. This image reconstruction was made by analysing the light collected from over three million distant galaxies more than 6 billion light-years away. Credit: Kilo-Degree Survey Collaboration/H. Hildebrandt & B. Giblin/ESO/N. Risinger (skysurvey.org). Music: Konstantino Polizois (soundcloud.com/konstantino-polizois).

In cosmic shear, it is not galaxy clusters but large-scale structures in the Universe that warp the light, which produces an even smaller effect. Very wide and deep surveys, such as KiDS, are needed to ensure that the very weak cosmic shear signal is strong enough to be measured and can be used by astronomers to map the distribution of gravitating matter. This study takes in the largest total area of the sky to ever be mapped with this technique so far.

Intriguingly, the results of their analysis appear to be inconsistent with deductions from the results of the European Space Agency’s Planck satellite, the leading space mission probing the fundamental properties of the Universe. In particular, the KiDS team’s measurement of how clumpy matter is throughout the Universe — a key cosmological parameter — is significantly lower than the value derived from the Planck data [3].

“This latest result indicates that dark matter in the cosmic web, which accounts for about one-quarter of the content of the Universe, is less clumpy than we previously believed.”

Dark matter remains elusive to detection, its presence only inferred from its gravitational effects. Studies like these are the best current way to determine the shape, scale and distribution of this invisible material.

The surprise result of this study also has implications for our wider understanding of the Universe, and how it has evolved during its almost 14-billion-year history. Such an apparent disagreement with previously established results from Planck means that astronomers may now have to reformulate their understanding of some fundamental aspects of the development of the Universe.

Hendrik Hildebrandt comments:

“Our findings will help to refine our theoretical models of how the Universe has grown from its inception up to the present day.”

The KiDS analysis of data from the VST is an important step but future telescopes are expected to take even wider and deeper surveys of the sky.

The co-leader of the study, Catherine Heymans of the University of Edinburgh in the UK adds:

“Unravelling what has happened since the Big Bang is a complex challenge, but by continuing to study the distant skies, we can build a picture of how our modern Universe has evolved.”

[Konrad Kuijken (Leiden Observatory, the Netherlands), who is principal investigator of the KiDS survey concludes: ]

“We see an intriguing discrepancy with Planck cosmology at the moment. Future missions such as the Euclid satellite and the Large Synoptic Survey Telescope will allow us to repeat these measurements and better understand what the Universe is really telling us,”

Notes

[1] The international KiDS team of researchers includes scientists from Germany, the Netherlands, the UK, Australia, Italy, Malta and Canada.

[2] This corresponds to about 450 square degrees, or a little more than 1% of the entire sky.

[3] The parameter measured is called S₈. Its value is a combination of the size of density fluctuations in, and the average density of, a section of the Universe. Large fluctuations in lower density parts of the Universe have an effect similar to that of smaller amplitude fluctuations in denser regions and the two cannot be distinguished by observations of weak lensing. The 8 refers to a cell size of 8 megaparsecs, which is used by convention in such studies.

NASA JPL’s What’s Up for December 2016 describes the most interesting sights to see in the night sky for the coming month:

See Mercury, Venus and Mars all month long and a New Year’s Eve comet. With some luck, you may catch some Geminid and Ursid meteors, too. Catch up on all of NASA’s missions at http://www.nasa.gov

The latest Hubble telescope finding:

Tangled threads weave through cosmic oddity

New observations from the NASA/ESA Hubble Space Telescope have revealed the intricate structure of the galaxy NGC 4696 in greater detail than ever before. The elliptical galaxy is a beautiful cosmic oddity with a bright core wrapped in system of dark, swirling, thread-like filaments.

Despite the cluster’s size, NGC 4696 still manages to stand out from its companions — it is the cluster’s brightest member, known for obvious reasons as the Brightest Cluster Galaxy . This puts it in the same category as some of the biggest and brightest galaxies known in the Universe.

This video zooms on NGC 4696, the largest galaxy in the Centaurus Cluster (galaxy cluster Abell 3526) as seen with the NASA/ESA Hubble Space Telescope. Credit: ESA/Hubble, NASA, ESO/Digitized Sky Survey 2 and S. Brunier. Music: John Dyson (from the album “Moonwind”). Acknowledgment: Davide De Martin

Even if NGC 4696 keeps impressive company, it has a further distinction: the galaxy’s unique structure. Previous observations have revealed curling filaments that stretch out from its main body and carve out a cosmic question mark in the sky (heic1013), the dark tendrils encircling a brightly glowing centre.

An international team of scientists, led by astronomers from the University of Cambridge, UK, have now used new observations from the NASA/ESA Hubble Space Telescope to explore this thread-like structure in more detail. They found that each of the dusty filaments has a width of about 200 light-years, and a density some 10 times greater than the surrounding gas. These filaments knit together and spiral inwards towards the centre of NGC 4696, connecting the galaxy’s constituent gas to its core.

This video pans over NASA/ESA Hubble Space Telescope observations of the massive galaxy NGC 4696, which lies about 150 million light-years from Earth. Credit: ESO/L. Calçada, Music Credit: Konstantino Polizois

In fact, it seems that the galaxy’s core is actually responsible for the shape and positioning of the filaments themselves. At the centre of NGC 4696 lurks an active supermassive black hole. This floods the galaxy’s inner regions with energy, heating the gas there and sending streams of heated material outwards.

It appears that these hot streams of gas bubble outwards, dragging the filamentary material with them as they go. The galaxy’s magnetic field is also swept out with this bubbling motion, constraining and sculpting the material within the filaments.

Understanding more about filamentary galaxies such as NGC 4696 may help us to better understand why so many massive galaxies near to us in the Universe appear to be dead; rather than forming newborn stars from their vast reserves of gas and dust, they instead sit quietly, and are mostly populated with old and aging stars. This is the case with NGC 4696. It may be that the magnetic structure flowing throughout the galaxy stops the gas from creating new stars.