Thursday, January 31, 2019

Hubble fortuitously discovers a new galaxy in the cosmic neighbourhood

The accidentally discovered galaxy Bedin I

Bedin 1 in NGC 6752

Globular cluster NGC 6752

Wide-field view of NGC 6752 (ground-based view)


Videos 
Zooming in on NGC 6752 and Bedin 1
Zooming in on NGC 6752 and Bedin 1

Flight to Bedin 1
Flight to Bedin 1


Astronomers using the NASA/ESA Hubble Space Telescope to study some of the oldest and faintest stars in the globular cluster NGC 6752 have made an unexpected finding. They discovered a dwarf galaxy in our cosmic backyard, only 30 million light-years away. The finding is reported in the journal Monthly Notices of the Royal Astronomical Society: Letters.

An international team of astronomers recently used the NASA/ESA Hubble Space Telescope to study white dwarf stars within the globular cluster NGC 6752. The aim of their observations was to use these stars to measure the age of the globular cluster, but in the process they made an unexpected discovery.
In the outer fringes of the area observed with Hubble’s Advanced Camera for Surveys a compact collection of stars was visible. After a careful analysis of their brightnesses and temperatures, the astronomers concluded that these stars did not belong to the cluster — which is part of the Milky Way — but rather they are millions of light-years more distant.

Our newly discovered cosmic neighbour, nicknamed Bedin 1 by the astronomers, is a modestly sized, elongated galaxy. It measures only around 3000 light-years at its greatest extent — a fraction of the size of the Milky Way. Not only is it tiny, but it is also incredibly faint. These properties led astronomers to classify it as a dwarf spheroidal galaxy.

Dwarf spheroidal galaxies are defined by their small size, low-luminosity, lack of dust and old stellar populations [1]. 36 galaxies of this type are already known to exist in the Local Group of Galaxies, 22 of which are satellite galaxies of the Milky Way.

While dwarf spheroidal galaxies are not uncommon, Bedin 1 has some notable features. Not only is it one of just a few dwarf spheroidals that have a well established distance but it is also extremely isolated. It lies about 30 million light-years from the Milky Way and 2 million light-years from the nearest plausible large galaxy host, NGC 6744. This makes it possibly the most isolated small dwarf galaxy discovered to date.

From the properties of its stars, astronomers were able to infer that the galaxy is around 13 billion years old — nearly as old as the Universe itself. Because of its isolation — which resulted in hardly any interaction with other galaxies — and its age, Bedin 1 is the astronomical equivalent of a living fossil from the early Universe.

The discovery of Bedin 1 was a truly serendipitous find. Very few Hubble images allow such faint objects to be seen, and they cover only a small area of the sky. Future telescopes with a large field of view, such as the WFIRST telescope, will have cameras covering a much larger area of the sky and may find many more of these galactic neighbours.


Notes

[1] While similar to dwarf elliptical galaxies in appearance and properties, dwarf spheroidal galaxies are in general approximately spherical in shape and have a lower luminosity.


More Information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The results were presented in the letter The HST Large Programme on NGC 6752. I. Serendipitous discovery of a dwarf galaxy in background, published in the journal Monthly Notices of the Royal Astronomical Society: Letters.

The international team of astronomers that carried out this study consists of L. R. Bedin (INAF-Osservatorio Astronomico di Padova, Italy), M. Salaris (Liverpool John Moores University, UK), R. M. Rich (University of California Los Angeles, USA), H. Richer (University of British Columbia), J. Anderson (Space Telescope Science Institute, USA), B. Bettoni (INAF-Osservatorio Astronomico di Padova, Italy), D. Nardiello (Università di Padova, Italy), A. P. Milone (Università di Padova, Italy), A. F. Marino (Università di Padova, Italy), M. Libralato (Space Telescope Science Institute, USA), A. Bellini (Space Telescope Science Institute, USA), A. Dieball (University of Bonn, Germany), P. Bergeron (Université de Montréal, Canada), A. J. Burgasser (University of California San Diego, USA), D. Apai (University of Arizona, USA).

Image credit: NASA, ESA, Bedin et al.


 Links


Contact

L. R. Bedin
INAF-Osservatorio Astronomico di Padova
Padua, Italy
Tel: +49 8293 413
Email: luigi.bedin@oapd.inaf.it

Mathias Jäger
ESA/Hubble, Public Information Officer
Garching, Germany
Tel: +49 176 62397500
Email: mjaeger@partner.eso.org



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Wednesday, January 30, 2019

NASA’s NICER Mission Maps ‘Light Echoes’ of New Black Hole

In this illustration of a newly discovered black hole named MAXI J1820+070, a black hole pulls material off a neighboring star and into an accretion disk. Above the disk is a region of subatomic particles called the corona. Credit: Aurore Simonnet and NASA’s Goddard Space Flight Center. Hi-res image

Scientists have charted the environment surrounding a stellar-mass black hole that is 10 times the mass of the Sun using NASA’s Neutron star Interior Composition Explorer (NICER) payload aboard the International Space Station. NICER detected X-ray light from the recently discovered black hole, called MAXI J1820+070 (J1820 for short), as it consumed material from a companion star. Waves of X-rays formed “light echoes” that reflected off the swirling gas near the black hole and revealed changes in the environment’s size and shape.

“NICER has allowed us to measure light echoes closer to a stellar-mass black hole than ever before,” said Erin Kara, an astrophysicist at the University of Maryland, College Park and NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who presented the findings at the 233rd American Astronomical Society meeting in Seattle. “Previously, these light echoes off the inner accretion disk were only seen in supermassive black holes, which are millions to billions of solar masses and undergo changes slowly. Stellar black holes like J1820 have much lower masses and evolve much faster, so we can see changes play out on human time scales.”

A paper describing the findings, led by Kara, appeared in the Jan. 10 issue of Nature and is available online.
Watch how X-ray echoes, mapped by NASA’s Neutron star Interior Composition Explorer (NICER) revealed changes to the corona of black hole MAXI J1820+070. Credits: NASA’s Goddard Space Flight Center. Download this video and related multimedia in HD formats from NASA Goddard's Scientific Visualization Studio

J1820 is located about 10,000 light-years away toward the constellation Leo. The companion star in the system was identified in a survey by ESA’s (European Space Agency) Gaia mission, which allowed researchers to estimate its distance. Astronomers were unaware of the black hole’s presence 
until March 11, 2018, when an outburst was spotted by the Japan Aerospace Exploration Agency’s Monitor of All-sky X-ray Image (MAXI), also aboard the space station. J1820 went from a totally unknown black hole to one of the brightest sources in the X-ray sky over a few days. NICER moved quickly to capture this dramatic transition and continues to follow the fading tail of the eruption.

“NICER was designed to be sensitive enough to study faint, incredibly dense objects called neutron stars,” said Zaven Arzoumanian, the NICER science lead at Goddard and a co-author of the paper. “We’re pleased at how useful it’s also proven in studying these very X-ray-bright stellar-mass black holes.”

A black hole can siphon gas from a nearby companion star into a ring of material called an accretion disk. Gravitational and magnetic forces heat the disk to millions of degrees, making it hot enough to produce X-rays at the inner parts of the disk, near the black hole. Outbursts occur when an instability in the disk causes a flood of gas to move inward, toward the black hole, like an avalanche. The causes of disk instabilities are poorly understood.

Above the disk is the corona, a region of subatomic particles around 1 billion degrees Celsius (1.8 billion degrees Fahrenheit) that glows in higher-energy X-rays. Many mysteries remain about the origin and evolution of the corona. Some theories suggest the structure could represent an early form of the high-speed particle jets these types of systems often emit.

Astrophysicists want to better understand how the inner edge of the accretion disk and the corona above it change in size and shape as a black hole accretes material from its companion star. If they can understand how and why these changes occur in stellar-mass black holes over a period of weeks, scientists could shed light on how supermassive black holes evolve over millions of years and how they affect the galaxies in which they reside.

One method used to chart those changes is called X-ray reverberation mapping, which uses X-ray reflections in much the same way sonar uses sound waves to map undersea terrain. Some X-rays from the corona travel straight toward us, while others light up the disk and reflect back at different energies and angles.

X-ray reverberation mapping of supermassive black holes has shown that the inner edge of the accretion disk is very close to the event horizon, the point of no return. The corona is also compact, lying closer to the black hole rather than over much of the accretion disk. Previous observations of X-ray echoes from stellar black holes, however, suggested the inner edge of the accretion disk could be quite distant, up to hundreds of times the size of the event horizon. The stellar-mass J1820, however, behaved more like its supermassive cousins.  

As they examined NICER’s observations of J1820, Kara’s team saw a decrease in the delay, or lag time, between the initial flare of X-rays coming directly from the corona and the flare’s echo off the disk, indicating that the X-rays traveled shorter and shorter distances before they were reflected. From 10,000 light-years away, they estimated that the corona contracted vertically from roughly 100 to 10 miles — that’s like seeing something the size of a blueberry shrink to something the size of a poppy seed at the distance of Pluto.

The NICER instrument installed on the International Space Station, as captured by a high-definition external camera on Oct. 22, 2018. Credits: NASA

“NICER’s observations of J1820 have taught us something new about stellar-mass black holes and about how we might use them as analogs for studying supermassive black holes and their effects on galaxy formation,” said co-author Philip Uttley, an astrophysicist at the University of Amsterdam. “We’ve seen four similar events in NICER’s first year, and it’s remarkable. It feels like we’re on the edge of a huge breakthrough in X-ray astronomy.”

NICER is an Astrophysics Mission of Opportunity within NASA's Explorer program, which provides frequent flight opportunities for world-class scientific investigations from space utilizing innovative, streamlined and efficient management approaches within the heliophysics and astrophysics science areas. NASA's Space Technology Mission Directorate supports the SEXTANT component of the mission, demonstrating pulsar-based spacecraft navigation.

“This is the first time that we’ve seen this kind of evidence that it’s the corona shrinking during this particular phase of outburst evolution,” said co-author Jack Steiner, an astrophysicist at the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research in Cambridge. “The corona is still pretty mysterious, and we still have a loose understanding of what it is. But we now have evidence that the thing that’s evolving in the system is the structure of the corona itself.”

To confirm the decreased lag time was due to a change in the corona and not the disk, the researchers used a signal called the iron K line created when X-rays from the corona collide with iron atoms in the disk, causing them to fluoresce. Time runs slower in stronger gravitational fields and at higher velocities, as stated in Einstein’s theory of relativity. When the iron atoms closest to the black hole are bombarded by light from the core of the corona, the X-ray wavelengths they emit get stretched because time is moving slower for them than for the observer (in this case, NICER).

Kara’s team discovered that J1820’s stretched iron K line remained constant, which means the inner edge of the disk remained close to the black hole — similar to a supermassive black hole. If the decreased lag time was caused by the inner edge of the disk moving even further inward, then the iron K line would have stretched even more.

These observations give scientists new insights into how material funnels in to the black hole and how energy is released in this process.

By Jeanette Kazmierczak
NASA’s Goddard Space Flight Center, Greenbelt, Md.

Editor: Rob Garner

 Source: NASA/NICER

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Tuesday, January 29, 2019

Active galaxies point to new physics of cosmic expansion

Active galaxies to measure cosmic expansion
Copyright ESA (artist's impression and composition); 
NASA/ESA/Hubble (background galaxies); CC BY-SA 3.0 IGO

Investigating the history of our cosmos with a large sample of distant ‘active’ galaxies observed by ESA’s XMM-Newton, a team of astronomers found there might be more to the early expansion of the Universe than predicted by the standard model of cosmology. 

According to the leading scenario, our Universe contains only a few percent of ordinary matter. One quarter of the cosmos is made of the elusive dark matter, which we can feel gravitationally but not observe, and the rest consists of the even more mysterious dark energy that is driving the current acceleration of the Universe’s expansion. 

This model is based on a multitude of data collected over the last couple of decades, from the cosmic microwave background, or CMB – the first light in the history of the cosmos, released only 380 000 years after the big bang and observed in unprecedented detail by ESA’s Planck mission – to more ‘local’ observations. The latter include supernova explosions, galaxy clusters and the gravitational distortion imprinted by dark matter on distant galaxies, and can be used to trace cosmic expansion in recent epochs of cosmic history – across the past nine billion years.  

A new study, led by Guido Risaliti of Università di Firenze, Italy, and Elisabeta Lusso of Durham University, UK, points to another type of cosmic tracer – quasars – that would fill part of the gap between these observations, measuring the expansion of the Universe up to 12 billion years ago.

Quasars are the cores of galaxies where an active supermassive black hole is pulling in matter from its surroundings at very intense rates, shining brightly across the electromagnetic spectrum. As material falls onto the black hole, it forms a swirling disc that radiates in visible and ultraviolet light; this light, in turn, heats up nearby electrons, generating X-rays. 

Supermassive black hole
Copyright ESA–C. Carreau

Three years ago, Guido and Elisabeta realised that a well-known relation between the ultraviolet and X-ray brightness of quasars could be used to estimate the distance to these sources – something that is notoriously tricky in astronomy – and, ultimately, to probe the expansion history of the Universe. 

Astronomical sources whose properties allow us to gauge their distances are referred to as ‘standard candles’.

The most notable class, known as ‘type-Ia’ supernova, consists of the spectacular demise of white dwarf stars after they have over-filled on material from a companion star, generating explosions of predictable brightness that allows astronomers to pinpoint the distance. Observations of these supernovas in the late 1990s revealed the Universe’s accelerated expansion over the last few billion years.

“Using quasars as standard candles has great potential, since we can observe them out to much greater distances from us than type-Ia supernovas, and so use them to probe much earlier epochs in the history of the cosmos,” explains Elisabeta.

With a sizeable sample of quasars at hand, the astronomers have now put their method into practice, and the results are intriguing.

XMM-Newton
Copyright ESA-C. Carreau

Digging into the XMM-Newton archive, they collected X-ray data for over 7000 quasars, combining them with ultraviolet observations from the ground-based Sloan Digital Sky Survey. They also used a new set of data, specially obtained with XMM-Newton in 2017 to look at very distant quasars, observing them as they were when the Universe was only about two billion years old. Finally, they complemented the data with a small number of even more distant quasars and with some relatively nearby ones, observed with NASA’s Chandra and Swift X-ray observatories, respectively.

“Such a large sample enabled us to scrutinise the relation between X-ray and ultraviolet emission of quasars in painstaking detail, which greatly refined our technique to estimate their distance,” says Guido.

The new XMM-Newton observations of distant quasars are so good that the team even identified two different groups: 70 percent of the sources shine brightly in low-energy X-rays, while the remaining 30 percent emit lower amounts of X-rays that are characterised by higher energies. For the further analysis, they only kept the earlier group of sources, in which the relation between X-ray and ultraviolet emission appears clearer.

“It is quite remarkable that we can discern such level of detail in sources so distant from us that their light has been travelling for more than ten billion years before reaching us,” says Norbert Schartel, XMM-Newton project scientist at ESA.

After skimming through the data and bringing the sample down to about 1600 quasars, the astronomers were left with the very best observations, leading to robust estimates of the distance to these sources that they could use to investigate the Universe’s expansion.



Supernova and quasar data
Investigating the expansion of the Universe with type-Ia supernovas and quasars
Copyright Courtesy of Elisabeta Lusso & Guido Risaliti (2019) Description 

“When we combine the quasar sample, which spans almost 12 billion years of cosmic history, with the more local sample of type-Ia supernovas, covering only the past eight billion years or so, we find similar results in the overlapping epochs,” says Elisabeta.

“However, in the earlier phases that we can only probe with quasars, we find a discrepancy between the observed evolution of the Universe and what we would predict based on the standard cosmological model.”

Looking into this previously poorly explored period of cosmic history with the help of quasars, the astronomers have revealed a possible tension in the standard model of cosmology, which might require the addition of extra parameters to reconcile the data with theory.

“One of the possible solutions would be to invoke an evolving dark energy, with a density that increases as time goes by,” says Guido.

Incidentally, this particular model would also alleviate another tension that has kept cosmologists busy lately, concerning the Hubble constant – the current rate of cosmic expansion. This discrepancy was found between estimates of the Hubble constant in the local Universe, based on supernova data – and, independently, on galaxy clusters – and those based on Planck’s observations of the cosmic microwave background in the early Universe.

“This model is quite interesting because it might solve two puzzles at once, but the jury is definitely not out yet and we’ll have to look at many more models in great detail before we can solve this cosmic conundrum,” adds Guido.

The team is looking forward to observing even more quasars in the future to further refine their results. Additional clues will also come from ESA’s Euclid mission, scheduled for a 2022 launch to explore the past ten billion years of cosmic expansion and investigate the nature of dark energy.

“These are interesting times to investigate the history of our Universe, and it’s exciting that XMM-Newton can contribute by looking at a cosmic epoch that had remained largely unexplored so far,” concludes Norbert.


Notes for Editors

“Cosmological constraints from the Hubble diagram of quasars at high redshifts” by G. Risaliti & E. Lusso is published in Nature Astronomy.



For further information, please contact:

 Guido Risaliti
Università di Firenze
INAF – Osservatorio Astrofisico di Arcetri
Firenze, Italy
Email: risaliti@arcetri.inaf.it

Elisabeta Lusso
Centre for Extragalactic Astronomy
Durham University, UK
Email: elisabeta.lusso@durham.ac.uk

Norbert Schartel
XMM-Newton Project Scientist
European Space Agency
Email: norbert.schartel@sciops.esa.int

Markus Bauer








ESA Science Communication Officer









Tel: +31 71 565 6799









Mob: +31 61 594 3 954









Email: markus.bauer@esa.int


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Saturday, January 26, 2019

As clouds fall apart, a new star is born

Image of the massive star cluster NGC 3603, obtained with the Very Large Telescope. It probably has evolved in the same way as the one just forming in G351.77-0.54, the object depicted in this work. © Image: ESO

New observations reveal the physics behind the formation of a massive star cluster

Using the ALMA observatory in Chile, a group of astronomers led by MPIA’s Henrik Beuther has made the most detailed observation yet of the way that a giant gas cloud fragments into dense cores, which then act as the birthplaces of stars. The astronomers found that the mechanisms for fragmentation are fairly straightforward, resulting from the combination of the cloud’s pressure and gravity. More complex features, such as magnetic lines or turbulence, play a smaller role than previously thought.


Stars are born when giant clouds of gas and dust collapse. Whenever one of the collapsing regions becomes hot and dense enough for nuclear fusion to set in, a star is born. For massive stars, i.e. those stars that exhibit more than eight times the mass of the Sun, that is only part of the picture, though. The biggest stars in the Universe are not born singly. They are born from massive clouds of molecular gas, which then form a cascade of fragments, with many of the fragments giving birth to a star.

Astronomers have long wondered whether this fragmentation-mode of forming stars requires different physical mechanisms than for lower-mass stars. Proposals include turbulent gas motion, which could destabilize a region and lead to quicker collapse, or magnetic fields that could stabilize and thus delay collapse.

The different mechanisms should leave tell-tale traces in regions where multiple stars are forming. The collapse that leads to the formation of high-mass stars takes place on a hierarchy of different levels. On the largest scales, star formation involves giant molecular clouds, which consist mostly of hydrogen gas and can reach sizes between a few dozen and more than a hundred light-years across. Within those clouds are slightly denser clumps, typically a few light-years across. Each clump contains one or more dense cores, less than a fifth of a light-year in diameter. Within each core, collapse leads to the formation of either a single star or multiple stars. Together, the stars produced in the cores of a single clump will form a star cluster.

Tell-tale scales of fragmentation

The scales of this fragmentation at multiple levels depend on the mechanisms involved. The simplest model can be written down using no more than high school physics: An ideal gas has a pressure that depends on its temperature and density. In a simplified gas cloud, assumed to have constant density, that pressure must be strong enough everywhere to balance the force of gravity (given by Newton’s law of gravity) – even in the center of the cloud, where the inward gravitation-induced push of all the surrounding matter is strongest. Write this condition down, and you will find that any such constant-density cloud can only have a maximum size. If a cloud is larger than this maximum, which is called the Jeans length, the cloud will fragment and collapse.

Is the fragmentation of young massive clusters really dominated by these comparatively straightforward processes? It doesn’t need to be, and some astronomers have constructed much more complex scenarios, which include the influence of turbulent gas motion and magnetic field lines. These additional mechanisms change the conditions for cloud stability, and typically increase the scales of the different types of fragment.

Different predictions for cloud sizes offer a way of testing the simple physics scenario against its more complex competitors. That is what Henrik Beuther and his colleagues set out to do when they observed the star formation region G351.77-0.54 in the Southern constellation Scorpius (The Scorpion). Previous observations had indicated that in this region, fragmentation could be caught in the act. But none of these observations had been powerful enough to show the smallest scale of interest for answering the question of fragmentation scales: the protostellar cores, let alone their sub-structure.

ALMA takes the most detailed look yet

Beuther and his colleagues were able to do more. They used the ALMA Observatory in the Atacama Desert in Chile. ALMA combines the simultaneous observations of up to 66 radio telescopes to achieve a resolution of down to 20 milli-arcseconds, which allows astronomers to discern details more than ten times smaller than with any previous radio telescope, and at unrivalled sensitivity – a combination that has already led to a number of breakthrough observations also in other fields.

Beuther and his colleagues used ALMA to study the high-mass star-forming region G351.77-0.54 down to sub-core scales smaller than 50 astronomical units (in other words, less than 50 times the average distance between the Earth and the Sun). As Beuther says: “This is a prime example of how technology drives astronomical progress. We could not have obtained our results without the unprecedented spatial resolution and sensitivity of ALMA.”

Their results, together with earlier studies of the same cloud at larger scales, indicate that thermal gas physics is winning the day, even when it comes to very massive stars: Both the sizes of clumps within the cloud and, as the new observations show, of cores within the clumps and even of some core substructures are as predicted by Jeans length calculations, with no need for additional ingredients. Beuther comments: “In our case, the same physics provides a uniform description. Fragmentation from the largest to the smallest scales seems to be governed by the same physical processes.”

Small accretion disks: a new challenge

Simplicity is always a boon for scientific descriptions. However, the same observations also provided a discovery that will keep astronomers on their collective toes. In addition to studying fragmentation, Beuther et al. had been looking to unravel the structure of nascent stars (“protostars”) within the cloud. Astronomers expect such a protostar to be surrounded by a swirling disk of gas, called the accretion disk. From the inner disk of the rim, gas falls onto the growing star, increasing its mass. In addition, magnetic fields produced by the motion of ionized gas and the gas itself interact to produce tightly focused streams called jets, which shoot out some of the matter into space perpendicular to that disk. Submillimeter light from those regions carries tell-tale signs (“Doppler-broadening of spectral lines”) of the motion of dust, which in turn traces the motion of gas. But where Beuther and his collaborators had hoped for a clear signature from an accretion disk, instead, he found mainly the signature of jets, cutting a comparatively smooth path through the surrounding gas. Evidently, the accretion disks are even smaller than astronomers had expected – a challenge for future observations at even greater spatial resolution.

The research described here was undertaken by Henrik Beuther, Aida Ahmadi, Joseph Mottram, Hendrik Linz, Thomas K. Henning and Rolf Kuiper (also University of Tübingen) in collaboration with Luke T. Maud (Leiden University and ESO), Andrew J. Walsh (Macquarie University), Katharine G. Johnston (University of Leeds) and Steve N. Longmore (Liverpool John Moores University).



Contacts

 Dr. Henrik Beuther
Max Planck Institute for Astronomy, Heidelberg
Phone:+49 6221 528-447
Email:beuther@mpia.de

 Dr. Markus Pössel
Press & Public Relations
Max Planck Institute for Astronomy, Heidelberg
Phone:+49 6221 528-261  
Email:pr@mpia.de


Original publicantion

 Beuther, H.; Ahmadi, A.; Mottram, J. C.; Linz, H.; Maud, L. T.; Henning, Th.; Kuiper, R.; Walsh, A. J.; Johnston, K. G.; Longmore, S. N.

High-mass star formation at sub-50 au scales

2019, Astronomy & Astrophysics, 621, A122
Source DOI


Related articles 



May 14, 2016

The interplay of magnetic fields and gravitation in the gas cloud lead to the birth of new stars. 






Further information

ALMA – the Atacama Large Millimetre Array

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Friday, January 25, 2019

A Fleeting Moment in Time

A Fleeting Moment in Time

Digitized Sky Survey image around the planetary nebula ESO 577-24
 
The planetary nebula ESO 577-24 in the constellation Virgo

Videos

ESOcast 191 Light: A Fleeting Moment in Time
ESOcast 191 Light: A Fleeting Moment in Time

Panning across the evanescent planetary nebula ESO 577-24
Panning across the evanescent planetary nebula ESO 577-24

Zooming in on ESO 577-24
Zooming in on ESO 577-24


The faint, ephemeral glow emanating from the planetary nebula ESO 577-24 persists for only a short time — around 10,000 years, a blink of an eye in astronomical terms. ESO’s Very Large Telescope captured this shell of glowing ionised gas — the last breath of the dying star whose simmering remains are visible at the heart of this image. As the gaseous shell of this planetary nebula expands and grows dimmer, it will slowly disappear from sight.

An evanescent shell of glowing gas spreading into space — the planetary nebula ESO 577-24 —  dominates this image [1]. This planetary nebula is the remains of a dead giant star that has thrown off its outer layers, leaving behind a small, intensely hot dwarf star. This diminished remnant will gradually cool and fade, living out its days as the mere ghost of a once-vast red giant star.

Red giants are stars at the end of their lives that have exhausted the hydrogen fuel in their cores and begun to contract under the crushing grip of gravity. As a red giant shrinks, the immense pressure reignites the core of the star, causing it to throw its outer layers into the void as a powerful stellar wind. The dying star’s incandescent core emits ultraviolet radiation intense enough to ionise these ejected layers and cause them to shine. The result is what we see as a planetary nebula — a final, fleeting testament to an ancient star at the end of its life [2].

This dazzling planetary nebula was discovered as part of the National Geographic Society  — Palomar Observatory Sky Survey in the 1950s, and was recorded in the Abell Catalogue of Planetary Nebulae in 1966 [3]. At around 1400 light years from Earth, the ghostly glow of ESO 577-24 is only visible through a powerful telescope. As the dwarf star cools, the nebula will continue to expand into space, slowly fading from view.

This image of ESO 577-24 was created as part of the ESO Cosmic Gems Programme, an initiative that produces images of interesting, intriguing, or visually attractive objects using ESO telescopes for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for scientific observations; nevertheless, the data collected are made available to astronomers through the ESO Science Archive.


Notes

[1] Planetary nebulae were first observed by astronomers in the 18th century — to them, their dim glow and crisp outlines resembled planets of the Solar System.

[2] By the time our Sun evolves into a red giant, it will have reached the venerable age of 10 billion years. There is no immediate need to panic, however — the Sun is currently only 5 billion years old.

[3] Astronomical objects often have a variety of official names, with different catalogues providing different designations. The formal name of this object in the Abell Catalogue of Planetary Nebulae is PN A66 36.


More Information

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 16 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a Strategic Partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.


Links


Contacts

Calum Turner
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Email: pio@eso.org

Source: ESO/News

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Thursday, January 24, 2019

Hubble Sees Plunging Galaxy Losing Its Gas

Credits:  NASA, ESA, M. Sun (University of Alabama), and W. Cramer and J. Kenney (Yale University)

Credits: Hubble image: NASA, ESA, M. Sun (University of Alabama), and W. Cramer and J. Kenney (Yale University) 
Subaru image: M. Yagi (National Astronomical Observatory of Japan)


The rough-and-tumble environment near the center of the massive Coma galaxy cluster is no match for a wayward spiral galaxy. New images from NASA's Hubble Space Telescope show a spiral galaxy being stripped of its gas as it plunges toward the cluster’s center. A long, thin streamer of gas and dust stretches like taffy from the galaxy's core and on into space. Eventually, the galaxy, named D100, will lose all of its gas and become a dead relic, deprived of the material to create new stars and shining only by the feeble glow of old, red stars.

"This galaxy stands out as a particularly extreme example of processes common in massive clusters, where a galaxy goes from being a healthy spiral full of star formation to a 'red and dead galaxy,'" said William Cramer of Yale University in New Haven, Connecticut, leader of the team using the Hubble observations. "The spiral arms disappear, and the galaxy is left with no gas and only old stars. This phenomenon has been known about for several decades, but Hubble provides the best imagery of galaxies undergoing this process."

Called "ram pressure stripping," the process occurs when a galaxy, due to the pull of gravity, falls toward the dense center of a massive cluster of thousands of galaxies, which swarm around like a hive of bees. During its plunge, the galaxy plows through intergalactic material, like a boat moving through water. The material pushes gas and dust from the galaxy. Once the galaxy loses all of its hydrogen gas — fuel for starbirth — it meets an untimely death because it can no longer create new stars. The gas-stripping process in D100 began roughly 300 million years ago.

In the massive Coma cluster this violent gas-loss process occurs in many galaxies. But D100 is unique in several ways. Its long, thin tail is its most unusual feature. The tail, a mixture of dust and hydrogen gas, extends nearly 200,000 light-years, about the width of two Milky Way galaxies. But the pencil-like structure is comparatively narrow, only 7,000 light-years wide.

"The tail is remarkably well-defined, straight and smooth, and has clear edges," explained team member Jeffrey Kenney, also of Yale University. "This is a surprise because a tail like this is not seen in most computer simulations. Most galaxies undergoing this process are more of a mess. The clean edges and filamentary structures of the tail suggest that magnetic fields play a prominent role in shaping it. Computer simulations show that magnetic fields form filaments in the tail's gas. With no magnetic fields, the tail is more clumpy than filamentary."

The researchers' main goal was to study star formation along the tail. Hubble's sharp vision uncovered the blue glow of clumps of young stars. The brightest clump in the middle of the tail contains at least 200,000 stars, triggered by the ongoing gas loss from the galaxy. However, based on the amount of glowing hydrogen gas contained in the tail, the team had expected Hubble to uncover three times more stars than it detected.

The Subaru Telescope in Hawaii observed the glowing tail in 2007 during a survey of the Coma cluster's galaxies. But the astronomers needed Hubble observations to confirm that the hot hydrogen gas contained in the tail was a signature of star formation.

"Without the depth and resolution of Hubble, it's hard to say if the glowing hydrogen-gas emission is coming from stars in the tail or if it's just from the gas being heated," Cramer said. "These Hubble visible-light observations are the first and best follow-up of the Subaru survey."

The Hubble data show that the gas-stripping process began on the outskirts of the galaxy and is moving in towards the center, which is typical in this type of mass loss. Based on the Hubble images, the gas has been cleared out all the way down to the central 6,400 light-years.

Within that central region, there is still a lot of gas, as seen in a burst of star formation. "This region is the only place in the galaxy where gas exists and star formation is taking place," Cramer said. "But now that gas is being stripped out of the center, forming the long tail."

Adding to this compelling narrative is another galaxy in the image that foreshadows D100's fate. The object, named D99, began as a spiral galaxy similar in mass to D100. It underwent the same violent gas-loss process as D100 is now undergoing, and is now a dead relic. All of the gas was siphoned from D99 between 500 million and 1 billion years ago. Its spiral structure has mostly faded away, and its stellar inhabitants consist of old, red stars. "D100 will look like D99 in a few hundred million years," Kenney said.

The Coma cluster is located 330 million light-years from Earth.

The team's results appear online in the January 8, 2019, issue of The Astrophysical Journal.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.


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Contact

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

William Cramer
Yale University, New Haven, Connecticut
william.cramer@yale.edu

Jeffrey Kenney
Yale University, New Haven, Connecticut
203-432-3013
jeff.kenney@yale.edu


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Birth of Massive Black Holes in the Early Universe Revealed

This image shows a 30,000 light-year region from the Renaissance Simulation, centered on a cluster of young galaxies that generate radiation (white) and metals (green) while heating the surrounding gas. A dark matter halo just outside this heated region forms three supermassive stars (inset), each one over 1,000 times the mass of our Sun. The stars will quickly collapse into massive black holes, and eventually supermassive black holes, over billions of years. Credits: Advanced Visualization Lab, National Center for Supercomputing Applications. Hi-res images

This image shows the inner 30 light-years of a dark matter halo in a cluster of young galaxies. The rotating gaseous disk breaks apart into three clumps that collapse under their own gravity to form supermassive stars. Credits: John Wise, Georgia Institute of Technology. Hi-res images

When the universe was still a baby – less than 1 billion years old – some of its stars turned into monster black holes. A key mystery in astronomy has been: why are there so many supermassive black holes in the early universe?

A new study, supported by funding from NASA, the National Science Foundation and a grant from the European Commission, suggests that massive black holes thrive when galaxies form very quickly. To make a galaxy, you need stars, which are born out of gas clouds, but also an invisible substance called dark matter, which acts as a glue to keep stars from flying away from the galaxy. If the dark matter’s “halo” structure grows quickly early in its life, the formation of stars is stifled. Instead a massive black hole can form before the galaxy takes shape. Black holes ravenously eat gas that would have otherwise produced new stars, and become larger and larger.

Previously, scientists theorized that powerful radiation from other galaxies muted the formation of stars in these young regions with massive black holes. But new simulations suggest that the rapid growth of galaxies is key to growing the black holes.

A black hole is an extremely dense astronomical object from which nothing can escape, not even light. When a star explodes in a supernova, a black hole can be left behind. Alternatively, a supermassive star can burn through its fuel quickly and turn into a black hole, no explosion needed. Scientists say this is how many massive black holes form in rapidly assembling proto-galaxies.

The simulation-based study, to be reported January 23rd in the journal Nature, also finds that massive black holes are much more common in the universe than previously thought.

Read more from Georgia Tech


Media Contact:

 Elizabeth Landau
NASA Headquarters, Washington
elandau@jpl.nasa.gov
(818) 359-3241

Editor: Karl Hille


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Wednesday, January 23, 2019

Seeds of Giant Galaxies formed in the Early Universe

Figure 1: A wide field-of-view false-color image of a massive quiescent galaxy taken by Surpime-Cam on the Subaru Telescope (main image) and a high resolution close-up (inset) by IRCS (Infrared Camera and Spectrograph) on the Subaru Telescope. The yellow circle shows the point spread function of this observation corrected with the AO188 adaptive optics system. (Credit: NAOJ)

An international research team has shown that the largest galaxies in the Universe may have started out as ultra-dense objects in the very early Universe that then expanded over time.

Modern galaxies show a wide diversity, including dwarf galaxies, irregular galaxies, spiral galaxies, and massive elliptical galaxies. This final type, massive elliptical galaxies, provides astronomers with a puzzle. Although they are the most massive galaxies with the most stars, almost all of their stars are old. At some time during the past the progenitors of massive elliptical galaxies must have rapidly formed many stars and then stopped for some reason.

Fortunately, the finite speed of light gives scientists a way to turn back the clock and view the early Universe. If a galaxy is located 12 billion light-years away, then light from that galaxy must have traveled for 12 billion years before it reached Earth. This means that the light we observe today must have left the galaxy 12 billion years ago. In other words the light is the image of what the galaxy looked like 12 billion years ago. By observing galaxies at various distances from Earth, astronomers can reconstruct the history of the Universe.

An international team including researchers from the National Astronomical Observatory of Japan (NAOJ), the University of Tokyo, and Copenhagen University used data from NAOJ's Subaru Telescope and other telescopes to search for galaxies located 12 billion light-years away. Among this sample they identified massive quiescent galaxies, meaning massive galaxies without active star formation, as the probable progenitors of modern giant elliptical galaxies. It is surprising that mature giant galaxies already existed very early, when the Universe was only about ~13% of its current age.

The team then used the Subaru Telescope to perform high resolution follow-up observations in near infrared for the 5 brightest massive quiescent galaxies located 12 billion light-years away.

The results show that although the massive quiescent galaxies are compact (only about 2% the size of the Milky Way) they are almost as heavy as modern galaxies. This means that to become modern giant elliptical galaxies they must puff up about 100 times in size, but only increase in mass by about 5 times. Comparing the observations to toy models, the team showed that this would be possible if the growth was driven, not by major mergers where two similar galaxies merge to form a larger one, but by minor mergers where a large galaxy cannibalizes smaller ones.

Figure 2: The stellar mass (x-axis) and size (y-axis) relation derived assuming that the most massive galaxies at each epoch are the progenitors of the modern most massive giant elliptical galaxies (red). Gray solid and dashed curves show the size evolution driven by many minor mergers and major mergers, respectively. (Credit: NAOJ)

"We are very excited about the implications of our findings," explains corresponding author Mariko Kubo, a post-doctoral researcher at NAOJ. "But we are now at the resolution limit of existing telescopes. The superior spatial resolution of the Thirty Meter Telescope currently under development will allow us to study the morphologies of distant galaxies more precisely. For more distant galaxies beyond 12 billion light-years, we need the next generation James Webb Space Telescope."

These results appeared as Kubo et al. 2018, "The Rest-frame Optical Sizes of Massive Galaxies with Suppressed Star Formation at z∼4" in the Astrophysical Journal on November 20, 2018. This research paper is also available as a preprint (Kubo et al., arXiv:1810.00543) on arxiv.org. This research is supported by KAKENHI Grant Numbers JP15K17617, JP16K17659, and JP18K13578.



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Tuesday, January 22, 2019

Astronomers Study Mysterious New Type of Cosmic Blast

ALMA and VLA images of AT2018cow at left; visible-light image of outburst in its host galaxy at right. Images not to same scale. Images of the blast itself do not indicate its size, but are the result of its brightness and the characteristics of the telescopes. Credit: Sophia Dagnello, NRAO/AUI/NSF; R. Margutti, W.M. Keck Observatory; Ho, et al. Hi-res image

Artist's conception of a cosmic blast with a "central engine," such as that suggested for AT2018cow. Black hole at center is pulling in material that forms a rapidly-rotating disk that radiates prolific amounts of energy and propels superfast jets of material from its poles. Jet encounters material surrounding the blast. Credit: Bill Saxton, NRAO/AUI/NSF. Hi-res image

Intensely studied event's characteristics are unprecedented

When astronomers discovered a cosmic explosion in a galaxy nearly 200 million light-years from Earth last June 16, they soon realized it was something different. While still debating the details, scientists now believe they may have gotten their first glimpse of the birth of a powerful phenomenon seen throughout the Universe.

The explosion was discovered by the ATLAS all-sky survey system in Hawaii, and immediately got the attention of astronomers. First, it was unusually bright for a supernova explosion — a common source of such outbursts. In addition, it brightened, then faded, much faster than expected.

Half a year later, “despite being one of the most intensely studied cosmic events in history, watched by astronomers all over the world, we still don’t know what it is,” said Anna Ho, of Caltech, who led a team using the Atacama Large Millimeter/submillimeter Array (ALMA), in Chile, among other telescopes. The object, dubbed AT2018cow, “heralds a new class” of energetic cosmic blasts, Ho added.

The explosion’s unusual characteristics “were enough to get everybody excited,” said Raffaella Margutti, of Northwestern University, who led a team that used telescopes ranging from gamma rays to radio waves, including the National Science Foundation’s Karl G. Jansky Very Large Array (VLA), to study the object. “In addition, AT2018cow’s distance of 200 million light-years, is nearby, by astronomical standards,” making it an excellent target for study, Margutti said.

Astronomers are presenting their findings about the object at the American Astronomical Society’s meeting in Seattle, Washington.

After watching the object and measuring its changing characteristics with a worldwide collection of ground-based and orbiting telescopes, scientists still are not sure exactly what it is, but they have two leading explanations. It may be, they suspect, either a very unusual supernova, or the shredding of a star that passed too close to a massive black hole, called a Tidal Disruption Event (TDE). Researchers are quick to point out, however, that the object’s characteristics don’t match previously-seen examples of either one.

“If it is a supernova, then it is unlike any supernova we have ever seen,” Ho said. The object’s range of colors, or spectrum, she said, “doesn’t look like a supernova at all.” In addition, it was brighter in millimeter waves — those seen by ALMA — than any other supernova.

It also differs from previously-seen Tidal Disruption Events.

“It’s off-center in its host galaxy,” Deanne Coppejans, of Northwestern University, said, meaning it can’t be a star shredded by the supermassive black hole at the galaxy’s center. “If it’s a TDE, then we need an intermediate mass black hole to do the shredding, and those are expected to form in stellar clusters,” Kate Alexander, an Einstein Fellow at Northwestern, added. The problem with that, she pointed out, is that AT2018cow appears to be inside a high-density interstellar medium, which “is difficult to reconcile with the density of gas in stellar clusters.”

Most of the researchers agree that AT2018cow’s behavior requires a central source of ongoing energy unlike those of other supernova explosions. The best candidate, they said, is a black hole that is drawing material from its surroundings. The inflowing material forms a rotating disk around the black hole and that disk radiates prolific amounts of energy. This is the type of “central engine” that powers quasars and radio galaxies throughout the Universe as well as smaller examples such as microquasars.

When a star much more massive than the Sun ceases thermonuclear fusion and collapses of its own gravity, producing a “normal” supernova explosion, no such central engine is produced. However, in the extreme cases called hypernovas, which produce gamma ray bursts, such a central engine produces the superfast jets of material that generate the gamma rays. That engine, however is very short-lived, lasting only a matter of seconds.

If such a central engine powered AT2018cow, it lasted for weeks, making this event distinct from the collapse-induced explosions of supernovas and the more-energetic such explosions that produce gamma ray bursts. In the case of a TDE, the “engine” would come to life as the black hole drew in material from the star shredded by its gravitational pull.

Alternatively, the “engine” resulting from a supernova explosion might be a rapidly-rotating neutron star with an extremely powerful magnetic field — a magnetar.

“We know from theory that black holes and neutron stars form when a star dies, but we’ve never seen them right after they are born. Never,” Margutti said.

“This is very exciting, since it would be the first time that astronomers have witnessed the birth of a central engine,” Ho said.

However, because of AT2018cow’s strange behavior, the verdict still is unclear, the scientists said. The central energy source could be a powerful shock wave hitting a dense shell of material at the object’s core. Either the strange supernova or the TDE explanation still is viable, Ho’s team said.

The astronomers look forward to more work on AT2018cow and to more objects like it.

“During the first few weeks, this object was very bright at millimeter wavelengths, so that means that, with ALMA now available, we may be able to find and study others,” Ho said. “The peak strength of the radio emission starts at ALMA wavelengths, and only moved to VLA wavelengths after a few weeks,” she added.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) in Taiwan and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.


Media Contact:

 Dave Finley, Public Information Officer
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