The lastest report from ESO (European Southern Observatory):

Supermassive Black Holes Feed on Cosmic Jellyfish

Observations of “Jellyfish galaxies” with ESO’s Very Large Telescope have revealed a previously unknown way to fuel supermassive black holes. It seems the mechanism that produces the tentacles of gas and newborn stars that give these galaxies their nickname also makes it possible for the gas to reach the central regions of the galaxies, feeding the black hole that lurks in each of them and causing it to shine brilliantly. The results appeared today in the journal Nature.

Observations of “Jellyfish galaxies” with ESO’s Very Large Telescope have revealed a previously unknown way to fuel supermassive black holes. It seems the mechanism that produces the tentacles of gas and newborn stars that give these galaxies their nickname also makes it possible for the gas to reach the central regions of the galaxies, feeding the black hole that lurks in each of them and causing it to shine brilliantly. This quick video explains the main points.

An Italian-led team of astronomers used the MUSE (Multi-Unit Spectroscopic Explorer) instrument on the Very Large Telescope (VLT) at ESO’s Paranal Observatory in Chile to study how gas can be stripped from galaxies. They focused on extreme examples of jellyfish galaxies in nearby galaxy clusters, named after the remarkable long “tentacles” of material that extend for tens of thousands of light-years beyond their galactic discs [1][2].

The tentacles of jellyfish galaxies are produced in galaxy clusters by a process called ram pressure stripping. Their mutual gravitational attraction causes galaxies to fall at high speed into galaxy clusters, where they encounter a hot, dense gas which acts like a powerful wind, forcing tails of gas out of the galaxy’s disc and triggering starbursts within it.

This visualisation shows a jellyfish galaxy in the three-dimensional view of the MUSE instrument on ESO’s Very Large Telescope. This combines the normal two-dimensional view with the third dimension of wavelength. This galaxy has undergone jam pressure stripping as it moves rapidly into the hot gas in a galaxy cluster, and streamers of gas and young stars are trailing behind it. These show up as the tentacles extending away from the galaxy as they have different velocities. A 3D interactive view of this galaxy is available. Credit: ESO/Callum Bellhouse and the GASP collaboration

Six out of the seven jellyfish galaxies in the study were found to host a supermassive black hole at the centre, feeding on the surrounding gas [3]. This fraction is unexpectedly high — among galaxies in general the fraction is less than one in ten.

“This strong link between ram pressure stripping and active black holes was not predicted and has never been reported before,” said team leader Bianca Poggianti from the INAF-Astronomical Observatory of Padova in Italy. “It seems that the central black hole is being fed because some of the gas, rather than being removed, reaches the galaxy centre.” [4]

This artist’s illustration shows a spiral galaxy falling into a galaxy cluster. The galaxy is undergoing a process known as ram pressure stripping, where streaks of bright gas are being dragged out into space by the diffuse hot gas that it is moving through. Credit: NASA, ESA, and M. Kornmesser Acknowledgements: Ming Sun (UAH) and Serge Meunier

A long-standing question is why only a small fraction of supermassive black holes at the centres of galaxies are active. Supermassive black holes are present in almost all galaxies, so why are only a few accreting matter and shining brightly? These results reveal a previously unknown mechanism by which the black holes can be fed.

Yara Jaffé, an ESO fellow who contributed to the paper explains the significance: “These MUSE observations suggest a novel mechanism for gas to be funnelled towards the black hole’s neighbourhood. This result is important because it provides a new piece in the puzzle of the poorly understood connections between supermassive black holes and their host galaxies.”

The current observations are part of a much more extensive study of many more jellyfish galaxies that is currently in progress.

“This survey, when completed, will reveal how many, and which, gas-rich galaxies entering clusters go through a period of increased activity at their cores,” concludes Poggianti. “A long-standing puzzle in astronomy has been to understand how galaxies form and change in our expanding and evolving Universe. Jellyfish galaxies are a key to understanding galaxy evolution as they are galaxies caught in the middle of a dramatic transformation.”

This visualisation shows a jellyfish galaxy in the three-dimensional view of the MUSE instrument on ESO’s Very Large Telescope. This combines the normal two-dimensional view with the third dimension of wavelength. This galaxy has undergone ram pressure stripping as it moves rapidly into the hot gas in a galaxy cluster, and streamers of gas and young stars are trailing behind it. These show up as the tentacles extending away from the galaxy as they have different velocities. A 3D interactive view of this galaxy is available. Credit: ESO/Callum Bellhouse and the GASP collaboration

Notes

[1] To date, just over 400 candidate jellyfish galaxies have been found.

[2] The results were produced as part of the observational programme known as GASP (GAs Stripping Phenomena in galaxies with MUSE), which is an ESO Large Programme aimed at studying where, how and why gas can be removed from galaxies. GASP is obtaining deep, detailed MUSE data for 114 galaxies in various environments, specifically targeting jellyfish galaxies. Observations are currently in progress.

[3] It is well established that almost every, if not every, galaxy hosts a supermassive black hole at its centre, between a few million and a few billion times as massive as our Sun. When a black hole pulls in matter from its surroundings, it emits electromagnetic energy, giving rise to some of the most energetic of astrophysical phenomena: active galactic nuclei (AGN).

[4] The team also investigated the alternative explanation that the central AGN activity contributes to stripping gas from the galaxies, but considered it less likely. Inside the galaxy cluster, the jellyfish galaxies are located in a zone where the hot, dense gas of the intergalactic medium is particularly likely to create the galaxy’s long tentacles, reducing the possibility that they are created by AGN activity. There is therefore stronger evidence that ram pressure triggers the AGN and not vice versa.

The Latest ESO (European Southern Observatory) report:

Hint of Relativity Effects in Stars Orbiting Supermassive Black Hole at Centre of Galaxy

A new analysis of data from ESO’s Very Large Telescope and other telescopes suggests that the orbits of stars around the supermassive black hole at the centre of the Milky Way may show the subtle effects predicted by Einstein’s general theory of relativity. There are hints that the orbit of the star S2 is deviating slightly from the path calculated using classical physics. This tantalising result is a prelude to much more precise measurements and tests of relativity that will be made using the GRAVITY instrument as star S2 passes very close to the black hole in 2018.

At the centre of the Milky Way, 26 000 light-years from Earth, lies the closest supermassive black hole, which has a mass four million times that of the Sun. This monster is surrounded by a small group of stars orbiting at high speed in the black hole’s very strong gravitational field. It is a perfect environment in which to test gravitational physics, and particularly Einstein’s general theory of relativity.

A team of German and Czech astronomers have now applied new analysis techniques to the very rich set of existing observations of the stars orbiting the black hole, accumulated using ESO’s Very Large Telescope (VLT) in Chile and others over the last twenty years [1]. They compare the measured star orbits to predictions made using classical Newtonian gravity as well as predictions from general relativity.

The team found suggestions of a small change in the motion of one of the stars, known as S2, that is consistent with the predictions of general relativity [2]. The change due to relativistic effects amounts to only a few percent in the shape of the orbit, as well as only about one sixth of a degree in the orientation of the orbit [3]. If confirmed, this would be the first time that a measurement of the strength of the general relativistic effects has been achieved for stars orbiting a supermassive black hole.

This artist’s impression video shows the orbits of three of the stars very close to the supermassive black hole at the centre of the Milky Way. Analysis of data from ESO’s Very Large Telescope and other telescopes suggests that the orbits of these stars show the subtle effects predicted by Einstein’s general theory of relativity. There are hints that the orbit of the star called S2 is deviating slightly from the path calculated using classical physics.

The end of this sequence highlights the tiny change in the orbit due to the relativistic effects. The position of the black hole is marked with a red cross. Credit: ESO/M. Parsa/L. Calçada

Marzieh Parsa, PhD student at the University of Cologne, Germany and lead author of the paper, is delighted:

“The Galactic Centre really is the best laboratory to study the motion of stars in a relativistic environment. I was amazed how well we could apply the methods we developed with simulated stars to the high-precision data for the innermost high-velocity stars close to the supermassive black hole.”

The high accuracy of the positional measurements, made possible by the VLT’s near-infrared adaptive optics instruments, was essential for the study [4]. These were vital not only during the star’s close approach to the black hole, but particularly during the time when S2 was further away from the black hole. The latter data allowed an accurate determination of the shape of the orbit and how it is changing under the influence of relativity.

“During the course of our analysis we realised that to determine relativistic effects for S2 one definitely needs to know the full orbit to very high precision,”

comments Andreas Eckart, team leader at the University of Cologne.

As well as more precise information about the orbit of the star S2, the new analysis also gives the mass of the black hole and its distance from Earth to a higher degree of accuracy [5].

Co-author Vladimir Karas from the Academy of Sciences in Prague, the Czech Republic, is excited about the future:

“It is very reassuring that S2 shows relativistic effects as expected on the basis of its proximity to the extreme mass concentration at the centre of the Milky Way. This opens up an avenue for more theory and experiments in this sector of science.”

This analysis is a prelude to an exciting period for observations of the Galactic Centre by astronomers around the world. During 2018 the star S2 will make a very close approach to the supermassive black hole. This time the GRAVITY instrument, developed by a large international consortium led by the Max-Planck-Institut für extraterrestrische Physik in Garching, Germany [6], and installed on the VLT Interferometer [7], will be available to help measure the orbit much more precisely than is currently possible.  Not only is GRAVITY, which is already making high-precision measurements of the Galactic Centre, expected to reveal the general relativistic effects very clearly, but also it will allow astronomers to look for deviations from general relativity that might reveal new physics.

Notes

[1] Data from the near-infrared NACO camera now at VLT Unit Telescope 1 (Antu) and the near-infrared imaging spectrometer SINFONI at the Unit Telescope 4 (Yepun) were used for this study. Some additional published data obtained at the Keck Observatory were also used.

[2] S2 is a 15-solar-mass star on an elliptical orbit around the supermassive black hole. It has a period of about 15.6 years and gets as close as 17 light-hours to the black hole — or just 120 times the distance between the Sun and the Earth.

[3] A similar, but much smaller, effect is seen in the changing orbit of the planet Mercury in the Solar System. That measurement was one of the best early pieces of evidence in the late nineteenth century suggesting that Newton’s view of gravity was not the whole story and that a new approach and new insights were needed to understand gravity in the strong-field case. This ultimately led to Einstein publishing his general theory of relativity, based on curved spacetime, in 1915.

When the orbits of stars or planets are calculated using general relativity, rather than Newtonian gravity, they evolve differently. Predictions of the small changes to the shape and orientation of orbits with time are different in the two theories and can be compared to measurements to test the validity of general relativity.

[4] An adaptive optics system compensates for the image distortions produced by the turbulent atmosphere in real time and allows the telescope to be used at much angular resolution (image sharpness), in principle limited only by the mirror diameter and the wavelength of light used for the observations.

[5] The team finds a black hole mass of 4.2 × 106 times the mass of the Sun, and a distance from us of 8.2 kiloparsecs, corresponding to almost 27 000 light-years.

[6] The University of Cologne is part of the GRAVITY team (http://www.mpe.mpg.de/ir/gravity) and contributed the beam combiner spectrometers to the system.

[7] GRAVITY First Light was in early 2016 and it is already observing the Galactic Centre.

Here is NASA JPL’s preview of the night sky for August:

And here is the Hubble Telescope Institute‘s August night preview:

 

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The Hubble Telescope observes two galaxies

Galactic David and Goliath

The gravitational dance between two galaxies in our local neighbourhood has led to intriguing visual features in both as witnessed in this new NASA/ESA Hubble Space Telescope image. The tiny NGC 1510 and its colossal neighbour NGC 1512 are at the beginning of a lengthy merger, a crucial process in galaxy evolution. Despite its diminutive size, NGC 1510 has had a significant effect on NGC 1512’s structure and amount of star formation.

Galaxies come in a range of shapes and sizes, and astronomers use this fact to classify them based on their appearance. NGC 1512, the large galaxy to the left in this image, is classified as a barred spiral, named after the bar composed of stars, gas and dust slicing through its centre. The tiny NGC 1510 to the right, on the other hand, is a dwarf galaxy. Despite their very different sizes, each galaxy affects the other through gravity, causing slow changes in their appearances.

This video zooms in from a view of the night sky, through the constellation of Horologium, to end on the NASA/ESA Hubble Space Telescope observations of the interacting galaxies NGC 1512 and NGC 1510. Credit: ESA/Hubble, Digitized Sky Survey, Nick Risinger (skysurvey.org) Music: Johan B Monell

The bar in NGC 1512 acts as a cosmic funnel, channelling the raw materials required for star formation from the outer ring into the heart of the galaxy. This pipeline of gas and dust in NGC 1512 fuels intense star birth in the bright, blue, shimmering inner disc known as a circumnuclear starburst ring, which spans 2400 light-years.

Both the bar and the starburst ring are thought to be at least in part the result of the cosmic scuffle between the two galaxies — a merger that has been going on for 400 million years.

This video pans over NASA/ESA Hubble Space Telescope observations of the interacting galaxies NGC 1512 and NGC 1510, about 30 million light-years from Earth. Despite the difference in size, each galaxy gravitationally affects the other. The ring of starburst and the bar in the centre of the large spiral galaxy NGC 1512 are both in part created by the gravity of the much smaller NGC 1510. The gas and dust in the smaller galaxy have been swirled up by NGC 1512. This kick-started star formation that is even more intense than in the large spiral galaxy. This causes the galaxy to glow with the blue hue that is indicative of hot new stars. Credit: ESA/Hubble, Digitized Sky Survey, Nick Risinger (skysurvey.org).  Music: Johan B Monell

NGC 1512, which has been observed by Hubble in the past, is also home to a second, more serene, star-forming region in its outer ring. This ring is dotted with dozens of HII regions, where large swathes of hydrogen gas are subject to intense radiation from nearby, newly formed stars. This radiation causes the gas to glow and creates the bright knots of light seen throughout the ring.

Remarkably, NGC 1512 extends even further than we can see in this image — beyond the outer ring — displaying malformed, tendril-like spiral arms enveloping NGC 1510. These huge arms are thought to be warped by strong gravitational interactions with NGC 1510 and the accretion of material from it. But these interactions are not just affecting NGC 1512; they have also taken their toll on the smaller of the pair.

The constant tidal tugging from its neighbour has swirled up the gas and dust in NGC 1510 and kick-started star formation that is even more intense than in NGC 1512. This causes the galaxy to glow with the blue hue that is indicative of hot new stars.

NGC 1510 is not the only galaxy to have experienced the massive gravitational tidal forces of NGC 1512. Observations made in 2015 showed that the outer regions of the spiral arms of NGC 1512 were indeed once part of a separate, older galaxy. This galaxy was ripped apart and absorbed by NGC 1512, just as it is doing now to NGC 1510.

Together, the pair demonstrate how interactions between galaxies, even if they are of very different sizes, can have a significant influence on their structures, changing the dynamics of their constituent gas and dust and even triggering starbursts. Such interactions between galaxies, and galaxy mergers in particular, play a key role in galactic evolution.