Tuesday, July 07, 2015

The dark side of galactic radio jets

Active galaxy, Hercules A, showing extensive radio jets 
Image credit: NRAO

Sample CMB lensing map (top) and radio overdensity map (bottom)


Cosmic microwave radiation points to invisible ‘dark matter’, marking the spot where jets of material travel at near light speed, according to an international team of astronomers. Lead author Rupert Allison of Oxford University presented their results yesterday (6 July) at the National Astronomy Meeting in Venue Cymru, Llandudno, Wales.

Currently, no one knows for sure what dark matter is made of, but it accounts for about 26% of the energy content of the Universe, with massive galaxies forming in dense regions of dark matter. Although invisible, dark matter shows up through its gravitational effect – a big blob of dark matter pulls in normal matter (like electrons, protons and neutrons) through its own gravity, eventually packing together to create stars and entire galaxies.

Many of the largest of these are ‘active’ galaxies with supermassive black holes in their cores. Some of the gas falling towards the black holes is ejected out as jets of particles and radiation. Observations made with radio telescopes show that these jets often stretch for millions of light years from their host galaxy – far larger in extent than the galaxy itself.

Scientists therefore expected that the jets would live in regions where there was an excess, higher-than-average concentration of dark matter. But since dark matter is invisible, testing this idea is not straightforward.

Einstein’s general theory of relativity describes how light feels the effect of gravitational fields, giving away the presence of dark matter through an effect known as ‘gravitational lensing’. Observing how dark matter distorts light allows astronomers to deduce its location and measure its mass.

The Universe also has an ideal reference map – the Cosmic Microwave Background (CMB) – covering the entire sky. This is a relic of the formation of the cosmos, and is a ‘snapshot’ of the universe as it was just 400,000 years after the Big Bang. The light from this epoch has taken more than 13 billion years to reach us.

Light coming from this very early time travels through most of the universe unimpeded. The lumpy dark matter, however, exerts a small gravitational tug on the light, deflecting it slightly from a straight-line path, rather like a lens does in a pair of glasses.

By analysing subtle distortions in the CMB, the team of Mr Allison, Dr Sam Lindsay (Oxford) and Dr Blake Sherwin (UC Berkeley) were able to locate dense regions of dark matter. As suspected, this is where the powerful radio jets are more common – a deep-lying correlation between the most massive galaxies today and the afterglow of the Big Bang.

Mr Allison commented: “Without dark matter, big galaxies wouldn’t have formed and supermassive black holes wouldn’t exist. And without black holes, we wouldn’t see intergalactic jets. So we have found another signature of how dark matter shapes today’s universe.”

The scientists now hope to use new instruments to improve their measurements and more clearly understand how radio jets and their host galaxies change over the history of the Universe. Future telescopes such as Advanced ACTPol (http://www.princeton.edu/act/) and the Square Kilometre Array (http://skatelescope.org) will provide the complementary data to make this hope a reality.




Media contacts

Robert Massey
Royal Astronomical Society
Mob: +44 (0)794 124 8035
rm@ras.org.uk

Ms Anita Heward
Royal Astronomical Society
Mob: +44 (0)7756 034 243
anitaheward@btinternet.com

Dr Sam Lindsay
Royal Astronomical Society
Mob: +44 (0) 7957 566 861
sl@ras.org.uk



Science contact

Mr Rupert Allison
University of Oxford
rupert.allison@astro.ox.ac.uk



Further information

Original scientific publication:
http://mnras.oxfordjournals.org/content/451/1/5368.abstract?keytype=ref&ijkey=YB50kzkZn1z4ivG
http://arxiv.org/abs/1502.06456


The researchers are part of a collaboration of scientists working on the Atacama Cosmology Telescope high in the Atacama Desert in Northern Chile (http://arxiv.org/find/all/1/ti:+AND+Telescope+AND+Cosmology+AND+The+Atacama/0/1/0/all/0/1).

They measured the lensing effect of dark matter on the Cosmic Microwave Background, and compared this to the positions of radio jets found using the Very Large Array radio telescope in New Mexico, USA (http://sundog.stsci.edu). http://www.princeton.edu/act/




Notes for editors

The Royal Astronomical Society National Astronomy Meeting (NAM 2015, http://nam2015.org) will take place at Venue Cymru, in Llandudno, Wales, from 5-9 July. NAM 2015 will be held in conjunction with the annual meetings of the UK Solar Physics (UKSP) and Magnetosphere Ionosphere Solar-Terrestrial physics (MIST) groups. The conference is principally sponsored by the Royal Astronomical Society (RAS) and the Science and Technology Facilities Council (STFC). Follow the conference on Twitter via @RASNAM2015

The Royal Astronomical Society (RAS, www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter via @royalastrosoc

The Science and Technology Facilities Council (STFC, www.stfc.ac.uk) is keeping the UK at the forefront of international science and tackling some of the most significant challenges facing society such as meeting our future energy needs, monitoring and understanding climate change, and global security. The Council has a broad science portfolio and works with the academic and industrial communities to share its expertise in materials science, space and ground-based astronomy technologies, laser science, microelectronics, wafer scale manufacturing, particle and nuclear physics, alternative energy production, radio communications and radar. It enables UK researchers to access leading international science facilities for example in the area of astronomy, the European Southern Observatory. Follow STFC on Twitter via @stfc_matters

Sterile neutrinos, shielded candles and modified gravity: cosmology looks beyond the standard model

Comparison of Cold Dark Matter (CDM) and sterile neutrino simulations of Milky Way-like dark matter haloes (the invisible “skeleton" within which the galaxy will actually form). Credit: M Lovell/ICC Durham. Click  here for an enlarged image


What are the mysterious dark matter and dark energy that seem to account for so much of our Universe? Why is the Universe expanding?  For the past 30 years, most cosmologists have looked to the ‘standard model’ to answer these questions, and have had wide-ranging success in simulating formation in the universe and matching observational data.  But not everything quite fits the predictions. Are these discrepancies down to the interpretation of observations, or is a more fundamental rethink required? On Tuesday 7th July, a special session at the National Astronomy Meeting (NAM) 2015 has been convened for astronomers to take stock of the evidence and stimulate further investigation of cosmology beyond the standard model.  

The most popular candidate for the elusive particles that give the Universe extra mass is Cold Dark Matter (CDM).  CDM particles are thought to move slowly compared to the speed of light and interact very weakly with electromagnetic radiation. However, no one has managed to detect CDM to date.  Sownak Bose from Durham University’s Institute for Computational Cosmology (ICC) will present new predictions at NAM 2015 for a different candidate for dark matter, the sterile neutrino, which may have been detected recently.

“The neutrinos are sterile in that they interact even more weakly than ordinary neutrinos; their predominant interaction is via gravity,” explained Bose. “The key difference with CDM is that just after the Big Bang, sterile neutrinos would have had comparatively larger velocities than CDM and would thus have been able to move in random directions away from where they were born. Structures in the sterile neutrino model are smeared out, compared to CDM, and the abundance of structures on small scales is reduced.  By modelling how the Universe has evolved from that starting point and looking at the distribution of present-day structures, such as dwarf-mass galaxies, we can test which model -- sterile neutrinos or CDM -- fits best with observations.”

Last year, two independent groups detected an unexplained emission line at X-ray wavelengths in clusters of galaxies using the Chandra and XMM-Newton X-ray telescopes.  The energy of the line fits with predictions for the energies at which sterile neutrinos would decay over the lifetime of the Universe.  Bose and colleagues from the ICC in Durham are using sophisticated models of galaxy formation to investigate whether sterile neutrino corresponding to such a signal could help zero-in on the true identity of dark matter.

“Our models show that a sterile neutrino with a mass corresponding to the signal detected would also be able to pass many current astrophysical tests of dark matter," said Bose. “We may have seen the first evidence for sterile neutrinos and this would be hugely exciting."

However, not everyone believes that extra mass from dark matter is needed to explain observations. Indranil Banik and colleagues at the University of St Andrews believe that a modified theory of gravity may be the answer.  Banik and colleagues have constructed a detailed model predicting velocities of galaxies in the local group, which is dominated by the mass of our own Milky Way and the neighbouring Andromeda galaxy. 

“On large scales, our Universe is expanding – galaxies further away are going away from us faster. But on local scales, the picture is more confusing,” said Banik.  “We found that running our model in the context of Newtonian gravity did not match the observations very well. Some local group galaxies are travelling outwards so fast that it’s as if the Milky Way and Andromeda are exerting no gravitational pull at all!”

The St Andrews group suggests that these fast-moving outliers could be explained by a gravitational boost from a close encounter between the Milky Way and Andromeda about 9 billion years ago. The very fast motions of the two galaxies as they flew past each other, at around 600 kilometres per second, would have caused gravitational slingshot effects on other galaxies in the local group.

“This is like the trick spacecraft use to build up speed to reach the outer planets in our Solar System. Essentially, the big object – in this case the Milky Way or Andromeda – is slowed down slightly by the gravity from a passing object – the dwarf galaxy – which greatly speeds up as it's much lighter. This fits our observations – but not predictions with Newtonian gravity. This is just not strong enough to be compatible with such a close encounter between the Milky Way and Andromeda. Thus, we believe that our work favours a modified gravity theory and adds to a growing body of evidence from observations of galaxies,” said Banik.

The amount of dark energy in the Universe is also a matter of debate. The first evidence for dark energy – an energy field causing the expansion of the Universe to accelerate – came through measurements of Type Ia supernovae, which are used by astronomers as cosmic lighthouses to determine distances. However, there is now increasing evidence that Type Ia supernovae are not ‘standard candles’ and the precise brightness reached by these exploding white dwarf stars depends on the environment in the host galaxy.  Now, Dr Heather Campbell and colleagues at the University of Cambridge have used the largest sample of supernovae and host galaxies to date to study the relation between host galaxy and supernova luminosity.

“Understanding the effect of the properties of the host is critical if astronomers are to make the most precise measurements possible of dark energy,” said Campbell.  “More massive galaxies tend to have fainter supernovae.  If the galaxy properties are not accounted for properly, then the amount of dark energy in the Universe is underestimated. This work is crucial for future telescopes and space missions such as LSST and Euclid, which will attempt to make precision measurements of the expansion of the Universe.”

The session convener, Prof Peter Coles said, “Although cosmology has made great progress in recent years, many questions remain unanswered and indeed many questions unasked. This meeting is a timely opportunity to look at some of the gaps in our current understanding and some of the ideas that are being put forward for how those gaps might be filled.”



Images and captions

Comparison of Cold Dark Matter (CDM) and sterile neutrino simulations of Milky Way-like dark matter haloes (the invisible “skeleton" within which the galaxy will actually form). The "Milky Way" would form somewhere near the centre (the yellowish bit), with its satellite galaxies distributed among the many of smaller haloes around it. On the left is a visualisation of the Milky Way environment in a Universe dominated by CDM; on the right is the same object seen in a sterile neutrino dark matter Universe. While there are thousands of satellite galaxies in the CDM model, their abundance is greatly reduced in the sterile neutrino case. The net result is a “smoother” halo in the sterile neutrino case, compared to the “lumpy” CDM one. The simulations were created at the Institute for Computational Cosmology in Durham as part of the Aquarius supercomputing project undertaken by the Virgo consortium.

Is this what the night sky looked like billions of years ago? Cosmologists from St Andrews think that the motion of outlying galaxies in the Local Group could be explained by a close encounter between the Milky Way and Andromeda 9 billion years ago.Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger

Type Ia supernovae, such as supernova 1994D in galaxy NGC 4526 (imaged here by the Hubble Space Telescope), are used as cosmic lighthouses by astronomers to measure distance in the Universe.  A team from the University of Cambridge has used the largest sample of supernovae and host galaxies to date to study the relation between host galaxy and the precise brightness of the supernova. Credit: NASA/ESA, The Hubble Key Project Team and The High-Z Supernova Search Team



Media contacts

Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)794 124 8035
rm@ras.org.uk

Ms Anita Heward
Royal Astronomical Society
Mob: +44 (0)7756 034 243
anitaheward@btinternet.com

Dr Sam Lindsay
Royal Astronomical Society
Mob: +44 (0) 7957 566 861
sl@ras.org.uk



Science contacts

Mr Sownak Bose
Institute for Computational Cosmology
Durham University
sownak.bose@durham.ac.uk

Dr Heather Campbell
Institute of Astronomy
University of Cambridge
hcc@ast.cam.ac.uk

Mr Indranil Banik
School of Physics and Astronomy
University of St Andrews
ib45@st-andrews.ac.uk

Prof Peter Coles
Head of School of Mathematical and Physical Sciences, Astronomy Centre
University of Sussex
P.Coles@sussex.ac.uk



Futher information

‘Dynamical History of the Local Group in LCDM’, Indranil Banik and Hongsheng Zhao. Submitted to Monthly Notices of the Royal Astronomical Society, June 2015.
http://arxiv.org/abs/1506.07569

Did Andromeda crash into the Milky Way 10 billion years ago?
http://www.ras.org.uk/news-and-press/224-news-2013/2303-did-andromeda-crash-into-the-milky-way-10-billion-years-ago



Note for editors


The Royal Astronomical Society National Astronomy Meeting (NAM 2015, http://nam2015.org) will take place in Llandudno, Wales, from 5-9 July. NAM 2015 will be held in conjunction with the annual meetings of the UK Solar Physics (UKSP) and Magnetosphere Ionosphere Solar-Terrestrial physics (MIST) groups. The conference is principally sponsored by the Royal Astronomical Society (RAS) and the Science and Technology Facilities Council (STFC). Follow the conference on Twitter via @RASNAM2015

The Royal Astronomical Society (RAS, www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter via @royalastrosoc

The Science and Technology Facilities Council (STFC, www.stfc.ac.uk) is keeping the UK at the forefront of international science and tackling some of the most significant challenges facing society such as meeting our future energy needs, monitoring and understanding climate change, and global security. The Council has a broad science portfolio and works with the academic and industrial communities to share its expertise in materials science, space and ground-based astronomy technologies, laser science, microelectronics, wafer scale manufacturing, particle and nuclear physics, alternative energy production, radio communications and radar. It enables UK researchers to access leading international science facilities for example in the area of astronomy, the European Southern Observatory. Follow STFC on Twitter via @stfc_matters

About Durham University

•             The Durham astronomy group, including the Centre for Extragalactic Astronomy, as well as the Institute for Computational Cosmology, is one of the leading research centres in the world and was ranked first in Europe and 6th in the world based on impact in the Space Sciences.
•             A world top 100 university with a global reputation and performance in research and education
•             A member of the Russell Group of leading research-intensive UK universities
•             Research at Durham shapes local, national and international agendas, and directly informs the teaching of our students
•             Ranked in the world’s top 100 universities for reputation (Times Higher Education World Reputation Review rankings 2015).
•             Ranked in the world top 25 for the employability of its students by blue-chip companies world-wide (QS World University Rankings 2014/15)
•             In the global top 50 for Arts and Humanities (THE World University Rankings 2013/14)
•             In the 2016 Complete University Guide, Durham was ranked fifth in the UK.
Durham was named as The Times and Sunday Times 'Sports University of the Year 2015' in recognition of outstanding performance in both the research and teaching of sport, and student and community participation in sport at all levels.

Rings and Loops in the stars: Planck’s stunning new images

An image of the ring around the star Lambda Orionis, made with the ESA Planck satellite. The ring, here seen in pink, is around 200 light years across. In the image red represents the anomalous microwave emission (AME), green represents the emission from interstellar plasma and the blue is emission arising from electrons moving in magnetic fields. Credit: M. Peel / JCBA / Planck / ESA. Click here for a full size image


A ring of dust 200 light years across and a loop covering a third of the sky: two of the results in a new map from the Planck satellite. Dr Mike Peel and Dr Paddy Leahy of the Jodrell Bank Centre for Astrophysics (JCBA) presented the images today at the National Astronomy Meeting (NAM 2015) at Venue Cymru, Llandudno, Wales.

The European Space Agency (ESA) Planck satellite, launched in 2009 to study the ancient light of the Big Bang, has also given us maps of our own Galaxy, the Milky Way, in microwaves (radiation at cm- to mm-wavelengths). Microwaves are generated by electrons spiralling in the Galaxy's magnetic field at nearly the speed of light (the synchrotron process); by collisions in interstellar plasma, by thermal vibration of interstellar dust grains, and by "anomalous" microwave emission (AME), which may be from spinning dust grains.

The relative strength of these processes changes with wavelength, and are separated using multi-wavelength measurements from Planck, from NASA's WMAP satellite, and from ground-based radio telescopes, giving maps of each component.

The new maps show regions covering huge areas of our sky that produce AME; this process, only discovered in 1997,  could account for a large amount of galactic microwave emission with a wavelength near 1 cm. One example where it is exceptionally bright is the 200 light year-wide dust ring around the Lambda Orionis nebula (the 'head' of the familiar Orion constellation). This is the first time the ring has been seen in this way.

A full sky map made using the ESA Planck satellite. Loop 1, marked by the dashed ellipse, is the yellow feature above centre, shading to purple, and the purple arc below centre. The colours represent the angle of the magnetic field and the brightness represents the signal strength. Credit: M. Peel / JCBA / Planck / ESA. Click here for a full size image


A wide field map also shows synchrotron loops and spurs (where charged particles spiral around magnetic fields), including the huge Loop 1, discovered more than 50 years ago. Remarkably, astronomers are still very uncertain about its distance – it could be anywhere between 400 and 25,000 light years away – and though it covers around a third of the sky it is impossible to say exactly how big it is.



Media contacts

Robert Massey
Royal Astronomical Society
Mob: +44 (0)794 124 8035
rm@ras.org.uk

Ms Anita Heward
Royal Astronomical Society
Mob: +44 (0)7756 034 243
anitaheward@btinternet.com

Dr Sam Lindsay
Royal Astronomical Society
Mob: +44 (0) 7957 566 861
sl@ras.org.uk



Science contacts

Dr Mike Peel
Jodrell Bank Centre for Astrophysics
michael.peel@manchester.ac.uk

Dr Paddy Leahy
Jodrell Bank Centre for Astrophysics
j.p.leahy@manchester.ac.uk

Prof Clive Dickinson
Jodrell Bank Centre for Astrophysics
clive.dickinson@manchester.ac.uk




Further information

The new work has been submitted to “Planck 2015 results. XXV. Diffuse low-frequency Galactic foregrounds”, the Planck Collaboration, Astronomy and Astrophysics. See the preprint of this paper


This research was supported by an ERC Starting (Consolidator) Grant (no. 307209) and STFC Consolidated Grant (no. ST/L000768/1).




Notes for editors


The Royal Astronomical Society  National Astronomy Meeting (NAM 2015) will take place in Llandudno, Wales, from 5-9 July. NAM 2015 will be held in conjunction with the annual meetings of the UK Solar Physics (UKSP) and Magnetosphere Ionosphere Solar-Terrestrial physics (MIST) groups. The conference is principally sponsored by the Royal Astronomical Society (RAS) and the Science and Technology Facilities Council (STFC). Follow the conference on Twitter.

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter

The Science and Technology Facilities Council (STFC) is keeping the UK at the forefront of international science and tackling some of the most significant challenges facing society such as meeting our future energy needs, monitoring and understanding climate change, and global security. The Council has a broad science portfolio and works with the academic and industrial communities to share its expertise in materials science, space and ground-based astronomy technologies, laser science, microelectronics, wafer scale manufacturing, particle and nuclear physics, alternative energy production, radio communications and radar. It enables UK researchers to access leading international science facilities for example in the area of astronomy, the European Southern Observatory. Follow STFC on Twitter

Jodrell Bank Centre for Astrophysics (JBCA) is directly involved with the two lowest frequencies of the Low Frequency Instrument, the 30 and 44 GHz radiometers. These have 4 and 6 detectors respectively, operating at 20K (-253.15°C or -423.67°F). The resolution on the sky is 33 and 27 arc minutes, and the sensitivity 1.6 and 2.4 micro K (over 12 months). The cryogenic low noise amplifiers which are the heart of the radiometers were developed at Jodrell Bank, with help from the National Radio Astronomy Observatory in Virginia, USA.

The work to understand the Galactic emission seen by Planck is being co-led from Jodrell Bank by Emeritus Profs Rod Davies and Clive Dickinson. A number of projects are led by Jodrell Bank scientists, including Profs Richard Davis and Clive Dickinson. Each of the 14 projects focusses on one aspect of the Galaxy as seen by Planck, including the electrons that gyrate in the Galactic magnetic field, the ionized gas that pervades the interstellar medium and the dust grains that emit across the entire frequency range that Planck is sensitive to. Jodrell Bank is also leading the calibration and identifying systematics in the LFI data.

Monday, July 06, 2015

Astronomers use cosmic gravity to create a Black-Hole-Scope

Gravitational lensing
Copyright: ESA/ATG medialab 
 
Simulated microlensing
Copyright: Courtesy of A. Neronov, ISDC, University of Geneva, Switzerland


The Integral, Fermi and Swift space observatories have used the magnifying power of a cosmic lens to explore the inner regions of a supermassive black hole. 

Gamma rays are highly energetic radiation emitted by some of the most extreme objects in our Universe. Jets of gamma rays moving at close to the speed of light stream from the areas around black holes, for example. These jets are thought to be emitted by superheated material spinning wildly as it is devoured by the hungry black hole. 

Our telescopes will never be powerful enough to reveal these inner regions, and scientists struggle to examine exactly how these jets are unleashed into the Universe.

“Because we can’t clearly see what’s going on, we don’t fully understand this behaviour,” says Andrii Neronov of the University of Geneva, Switzerland, lead author on the Nature Physics paper published online today. 

“However, our method allowed us to ‘resolve’ this region, and get an insight into the patch of space directly surrounding a supermassive black hole known as PKS 1830-211.” 

This black hole lies many billions of light-years away. Neither ESA’s Integral satellite nor NASA’s Fermi gamma-ray telescope can observe the region unaided, but a lucky coincidence provides a helping hand: gravitational microlensing. 

“From Earth, black holes are tiny. They’re just so very far away,” notes Dr Neronov. “Trying to observe PKS 1830-211 is like trying to look at an ant sitting on the Moon. 

“None of our telescopes can observe something so small, so we used a trick to resolve the ant: a huge gravitational lens.” 

Massive cosmic objects, from single stars to galaxy clusters, bend and focus the light that flows around them with their gravity, acting like giant magnifying glasses. 

Dr Neronov and colleagues used a star sitting between their target and Earth to ‘zoom in’ to the black hole and measure the size of the jet-emitting region – the first time this method has ever been used with gamma rays. 

They picked out structures on the same angular scale as that of the Moon ant. The observed patch of sky covers a region about 100 times the Earth–Sun distance. In astronomical terms, this is remarkably small. 

“Our observations demonstrate that the gamma rays come from the direct vicinity of the black hole itself,” says Dr Neronov. “This gives us some idea about what is and isn’t important in generating the jets. 

“It’s amazing to be able to see such tiny things at such enormous distances from us. I’m very excited to have a ‘black-hole-scope’ to investigate the inner regions of the jets.”

Observing the gamma-ray source with ESA’s Integral and NASA’s Fermi and Swift allowed the astronomers to build up a more complete picture of the radiation streaming out. 

The more energetic gamma rays, detected by Fermi, are seen to be coming from the tiny base of the jet – the ‘ant on the Moon’-size region – while the lower energy gamma rays, detected by Integral, were emitted from a much larger surrounding region. 

The team also studied X-rays using Integral and Swift. They found these X-rays to be emanating from a region stretching around the hole some 400 billion km or more. 

“This black hole is one of the most powerful known objects of its kind. Fully characterising its emission will hopefully give us real insight into how these jets form,” says Erik Kuulkers, ESA’s Integral project scientist.
“Fortunately, the black hole lies in the field of space located towards the centre of our Galaxy, so Integral sees it often. 

“These observations provide unique information about the high-energy processes taking place around supermassive black holes, by allowing us to ‘look inside’ tiny structures lying very far away from us.” 


Notes for Editors

The results described here are reported in “Central engine of a gamma-ray blazar resolved through the “magnifying glass” of gravitational microlensing,” by A. Neronov, I. Vovk and D. Malyshev, published online in Nature Physics on 6 July.  


For further information, please contact:

Markus Bauer







ESA Science and Robotic Exploration Communication Officer








Tel: +31 71 565 6799








Mob: +31 61 594 3 954








Email:
markus.bauer@esa.int 

Andrii Neronov
ISDC, Astronomy Department
University of Geneva
Switzerland
Tel: +41 22 379 2120
Email:
Andrii.Neronov@unige.ch

Erik Kuulkers
Integral Project Scientist
Directorate of Science and Robotic Exploration
European Space Agency
Tel: +34 918 131 358
Mob: +34 699 439 987
Email:
erik.Kuulkers@sciops.esa.int

Source: ESA


Astronomers Predict Fireworks from Rare Stellar Encounter in 2018


Astronomers are gearing up for high-energy fireworks coming in early 2018, when a stellar remnant the size of a city meets one of the brightest stars in our galaxy. The cosmic light show will occur when a pulsar discovered by NASA's Fermi Gamma-ray Space Telescope swings by its companion star. Scientists plan a global campaign to watch the event from radio wavelengths to the highest-energy gamma rays detectable.


The pulsar, known as J2032+4127 (J2032 for short), is the crushed core of a massive star that exploded as a supernova. It is a magnetized ball about 12 miles across, or about the size of Washington, weighing almost twice the sun's mass and spinning seven times a second. J2032's rapid spin and strong magnetic field together produce a lighthouse-like beam detectable when it sweeps our way. Astronomers find most pulsars through radio emissions, but Fermi's Large Area Telescope (LAT) finds them through pulses of gamma rays, the most energetic form of light.

J2032 was found in 2009 through a so-called blind search of LAT data. Using this technique, astronomers can find pulsars whose radio beams may not be pointed precisely in our direction and are therefore much harder to detect.

"Two dozen pulsars were discovered this way in the first year of LAT data alone, including J2032," said David Thompson, a Fermi deputy project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Nearly all of them would not have been found without Fermi."

Once they knew exactly where to look, radio astronomers also were able to detect J2032. A team at the Jodrell Bank Centre for Astrophysics at the University of Manchester in the U.K. kept tabs on the object from 2010 through 2014. And they noticed something odd.

"We detected strange variations in the rotation and the rate at which the rotation slows down, behavior we have not seen in any other isolated pulsar," said Andrew Lyne, professor of physics at the University of Manchester. "Ultimately, we realized these peculiarities were caused by motion around another star, making this the longest-period binary system containing a radio pulsar."

The massive star tugging on the pulsar is named MT91 213. Classified as a Be star, the companion is 15 times the mass of the sun and shines 10,000 times brighter. Be stars drive strong outflows, called stellar winds, and are embedded in large disks of gas and dust.

"When we discovered this pulsar in 2009, we noticed that it was in the same direction as this massive star in the constellation Cygnus, but our initial measurements did not give any evidence that either star was a member of a binary system," explained Paul Ray, an astrophysicist at the Naval Research Laboratory in Washington. "The only way to escape that conclusion was if the binary system had a very long orbital period, much longer than the longest known pulsar-massive star binary at the time, which seemed unlikely."

Following an elongated orbit lasting about 25 years, the pulsar passes closest to its partner once each circuit. Whipping around its companion in early 2018, the pulsar will plunge through the surrounding disk and trigger astrophysical fireworks. It will serve as a probe to help astronomers measure the massive star's gravity, magnetic field, stellar wind and disk properties.     

Several features combine to make this an exceptional binary. Out of six similar systems where the massive star uses hydrogen as its central energy source, J2032's has the greatest combined mass, the longest orbital period, and, at a distance of about 5,000 light-years, is closest to Earth.

"This forewarning of the energetic fireworks expected at closest approach in three years' time allows us to prepare to study the system across the entire electromagnetic spectrum with the largest telescopes," added Ben Stappers, a professor of astrophysics at the University of Manchester. 

Astronomers think the supernova explosion that created the pulsar also kicked it into its eccentric orbit, nearly tearing the binary apart in the process. A study of the system led by Lyne and including Ray and Stappers was published June 16 in the journal Monthly Notices of the Royal Astronomical Society.


Related Links



Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.
Editor: Rob Garner 

 Source: NASA/Stars

Saturday, July 04, 2015

Counting Stars with Gaia

Copyright: ESA/Gaia – CC BY-SA 3.0 IGO
Stellar density map - Annotaded


This image, based on housekeeping data from ESA’s Gaia satellite, is no ordinary depiction of the heavens. While the image portrays the outline of our Galaxy, the Milky Way, and of its neighbouring Magellanic Clouds, it was obtained in a rather unusual way. 

As Gaia scans the sky to measure positions and velocities of a billion stars with unprecedented accuracy, for some stars it also determines their speed across the camera’s sensor. This information is used in real time by the attitude and orbit control system to ensure the satellite’s orientation is maintained with the desired precision. 

These speed statistics are routinely sent to Earth, along with the science data, in the form of housekeeping data. They include the total number of stars, used in the attitude-control loop, that is detected every second in each of Gaia’s fields of view. 

It is the latter – which is basically an indication of the density of stars across the sky – that was used to produce this uncommon visualisation of the celestial sphere. Brighter regions indicate higher concentrations of stars, while darker regions correspond to patches of the sky where fewer stars are observed. 

The plane of the Milky Way, where most of the Galaxy’s stars reside, is evidently the brightest portion of this image, running horizontally and especially bright at the centre. Darker regions across this broad strip of stars, known as the Galactic Plane, correspond to dense, interstellar clouds of gas and dust that absorb starlight along the line of sight. 

The Galactic Plane is the projection on the sky of the Galactic disc, a flattened structure with a diameter of about 100 000 light-years and a vertical height of only 1000 light-years. 

Beyond the plane, only a few objects are visible, most notably the Large and Small Magellanic Clouds, two dwarf galaxies orbiting the Milky Way, which stand out in the lower right part of the image. 

A few globular clusters – large assemblies up to millions of stars held together by their mutual gravity – are also sprinkled around the Galactic Plane. Globular clusters, the oldest population of stars in the Galaxy, sit mainly in a spherical halo extending up to 100 000 light-years from the centre of the Milky Way. 

The globular cluster NGC 104 is easily visible in the image, to the immediate left of the Small Magellanic Cloud. Other globular clusters are highlighted in an annotated version of this image. 

Interestingly, the majority of bright stars that are visible to the naked eye and that form the familiar constellations of the sky are not accounted for in this image because they are too bright to be used by Gaia’s control system. Similarly, the Andromeda galaxy – the largest galactic neighbour of the Milky Way – also does not stand out here. 

Counterintuitively, while Gaia carries a billion-pixel camera, it is not a mission aimed at imaging the sky: it is making the largest, most precise 3D map of our Galaxy, providing a crucial tool for studying the formation and evolution of the Milky Way.

Source: ESA





About Gaia

Gaia is an ESA mission to survey one billion stars in our Galaxy and local galactic neighbourhood in order to build the most precise 3D map of the Milky Way and answer questions about its origin and evolution.
Gaia’s scientific operations begun on 25 July 2014 with the special scanning through a narrow region in the sky, while the normal scanning procedure was switched on a month later, on 25 August. 

The mission’s primary scientific product will be a catalogue with the position, motion, brightness and colour of the surveyed stars. An intermediate version of the catalogue will be released in 2016. In the meantime, Gaia's observing strategy, with repeated scans of the entire sky, will allow the discovery and measurement of transient events across the sky. 

Acknowledgement: this image was prepared by Edmund Serpell, a Gaia Operations Engineer working in the Mission Operations Centre at ESA’s European Space Operations Centre in Darmstadt, Germany.
 
This image is licenced under the Creative Commons Attribution-ShareAlike 3.0 IGO (CC BY-SA 3.0 IGO) licence.


Friday, July 03, 2015

The Birth of a Planet

In the gas and dusk disk around HD100546 a planet is born. On the close up view (right) the star has been masked out during the data analysis.
Credit: Sascha Quanz/ETHZ


Astronomers of PlanetS have confirmed the existence of a young gas giant planet that is still embedded in the gas and dust rich disk around its young host star. For the first time scientists are now able to directly study the planet formation process at a very early stage.

For a full night a high-resolution infrared camera at the Very Large Telescope (VLT) in Chile observed only one object although telescope time at the European Southern Observatory (ESO) on Mount Paranal is very precious. Analysing the dataset collected by the instrument called NACO, an international team led by Sascha Quanz of ETH Zurich was able to confirm its earlier hypothesis: a giant planet candidate is orbiting the star named HD 100546. «The object is still in the process of formation and possibly surrounded by a disk from which it continues gathering material,» explains Sascha Quanz. The study that is published in the «Astrophysical Journal» has been carried out within the frame of the Swiss National Centre for Competence in Research (NCCR) PlanetS.

To confirm the existence of the young candidate planet the researchers analysed the data taken at three different infrared wavelengths. The planet – simply called HD 100546 b – is the first object of this kind ever detected. «It provides unique observational data related to the formation process of a gas giant planet,» says Sascha Quanz. So far, astronomers have found two other young stars that are thought to harbour young gas giant planets, but these objects appear to be in a slightly more advanced evolutionary stage as they already have cleared out large gaps in the disks they are embedded in.

Cosmic Laboratory

«Our object, however, appears to be still heavily embedded in dust and gas,» explains the researcher. How, where and when giant planets form in the disks around young stars was so far mainly addressed via theoretical considerations and computer simulations. «Now we have a ‘laboratory’ from which we can obtain empirical information,» says Sascha Quanz. HD 100546 is a young star. In astronomical terms this means that the object is «only» five to ten million years old. Located 335 light-years from Earth it is a relatively nearby cosmic neighbour.

The formation of a giant gas planet (right) near the star HD 100546 (left) is not yet complete, allowing astronomers to observe the process. 
Artist’s impression: ESO/L. Calçada. Hi-res image


The star is surrounded by a large gas and dust disk extending out to more than 300 times the distance between the Earth and the Sun. The young planet orbits its host star in the outer region of the disk about 50 times further away from its star than the Earth travels around the Sun. Current theories cannot easily explain the formation of a giant gas planet in this region. Therefore the new discovery poses a challenge to the researchers. One of many questions is: Was the young planet always in its current position or did it migrate outwards? Since the Swiss astronomers Michel Mayor and Didier Queloz have discovered the first exoplanet around a solar-type star twenty years ago, new theories about planetary formation have been developed including possible migration processes to explain why gas giant exoplanets can be detected orbiting their host stars in very close orbits.

Second candidate suggested

Previous observations of HD 100546 suggested that there might be an additional planet orbiting the star in a distance about five times closer to the star than the now confirmed young planet is. Therefore astronomers might even be able to study the formation of multiple gas giant planets in the same system even though the inner planet still needs further confirmation. Many of the almost 2000 exoplanets detected so far are part of multiple planet systems as our own solar system.

In 2013 Sascha Quanz and his team had already suggested the possible existence of the young planet in the disk surrounding HD 100546 in a first research paper. But at that time other explanations were still possible. With the new data the scientists now rule out that the detected signal could have come from a background source and a first estimate of the temperature and size of the object could be derived. «The observed properties are indeed best explained with a young, forming planet embedded in the disk around its host star,» the researcher conclude. Future observations with the array of radio telescopes called ALMA situated in the Chilean Atacama desert should confirm the existence of the suspected disk surrounding the forming planet and constrain its extent and mass. (bva)

Literature reference

Quanz SP, Amara A, Meyer MR, Girard JH, Kenworthy MA, Kasper M: Confirmation and characterization of the protoplanet HD 100546 b, Astrophysical Journal, 2015. doi:10.1088/0004-637X/807/1/64


Intense and short-lived Credit: ESA/Hubble & NASA

SBS 1415+437 or SDSS CGB 12067.1
Credit:  ESA/Hubble & NASA


This NASA/ESA Hubble Space Telescope picture shows a galaxy named SBS 1415+437 or SDSS CGB 12067.1, located about 45 million light-years from Earth. SBS 1415+437 is a Wolf–Rayet galaxy, a type of starbursting galaxy with an unusually high number of extremely hot and massive stars known as Wolf–Rayet stars.

These stars can be around 20 times as massive as the Sun, but seem to be on a mission to shed surplus mass as quickly as possible — they blast substantial winds of particles out into space, causing them to dwindle at a rapid rate. A typical star of this type can lose a mass equal to that of our Sun in just 100 000 years!

These massive stars are also incredibly hot, with surface temperatures some 10 to 40 times that of the Sun, and very luminous, glowing at tens of thousands to several million times the brightness of the Sun. Many of the brightest and most massive stars in the Milky Way are Wolf–Rayet stars.

Because these stars are so intense they do not last very long, burning up their fuel and blasting their bulk out into the cosmos on very short timescale ‒ only a few hundred thousand years. Because of this it is unusual to find more than a few of these stars per galaxy — except in Wolf–Rayet galaxies, like the one in this image.


Thursday, July 02, 2015

NGC 1333: Stellar Sparklers That Last

NGC 1333
Credit X-ray: NASA/CXC/SAO/S.Wolk et al; 
Optical: DSS & NOAO/AURA/NSF; Infrared: NASA/JPL-Caltech

JPEG (616.6 kb) - Large JPEG (4.4 MB) - Tiff (12.1 MB) - More Images


A Tour of NGC 6388



While fireworks only last a short time here on Earth, a bundle of cosmic sparklers in a nearby cluster of stars will be going off for a very long time. NGC 1333 is a star cluster populated with many young stars that are less than 2 million years old, a blink of an eye in astronomical terms for stars like the Sun expected to burn for billions of years.

This new composite image combines X-rays from NASA's Chandra X-ray Observatory (pink) with infrared data from the Spitzer Space Telescope (red) as well as optical data from the Digitized Sky Survey and the National Optical Astronomy Observatory Mayall 4-meter telescope on Kitt Peak (red, green, blue). The Chandra data reveal 95 young stars glowing in X-ray light, 41 of which had not been identified previously using infrared observations with Spitzer because they lacked infrared emission from a surrounding disk.

To make a detailed study of the X-ray properties of young stars, a team of astronomers, led by Elaine Winston from the University of Exeter, analyzed both the Chandra X-ray data of NGC 1333, located about 780 light years from Earth, and of the Serpens cloud, a similar cluster of young stars about 1100 light years away. They then compared the two datasets with observations of the young stars in the Orion Nebula Cluster, perhaps the most-studied young star cluster in the Galaxy.

The researchers found that the X-ray brightness of the stars in NGC 1333 and the Serpens cloud depends on the total brightness of the stars across the electromagnetic spectrum, as found in previous studies of other clusters. They also found that the X-ray brightness mainly depends on the size of the star. In other words, the bigger the stellar sparkler, the brighter it will glow in X-rays.

These results were published in the July 2010 issue of the Astronomical Journal and are available online. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado.


Fast Facts for NGC 1333:

Scale: Image is 18 arcmin across (about 4 light years)
Category: Normal Stars & Star Clusters
Coordinates (J2000): RA 03h 29m 02.00s | Dec +31 20 54.00
Constellation: Perseus
Observation Date: 12 Jul 2000, 05, 11 Jul 2006
Observation Time: 36 hours 7 min (1 day 12 hours 7 min).
Obs. ID: 642, 6436, 6437
Instrument: ACIS
References: Rebull, L.M., 2015, AJ (accepted); arXiv:1504.07564
Color Code: X-ray (Pink); Optical (Red, Green, Blue); Infrared (Red)
Distance Estimate: About 770 light years



Active pits on comet

Active pits on comet
Copyright; ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; 
graphic from J-B Vincent et al (2015). Hi-res image


Left: 18 pits have been identified in high-resolution OSIRIS images of Comet 67P/Churyumov–Gerasimenko’s northern hemisphere. The pits are named after the region they are found in, and some of them are active. The context image was taken on 3 August 2014 by the narrow-angle camera from a distance of 285 km; the image resolution is 5.3 m/pixel.  

Middle, top: close-up of the active pit named Seth_01 reveals small jets emanating from the interior walls of the pit. The close-up also shows the complex internal structure of the comet. The image is a section of an OSIRIS wide-angle camera image capture on 20 October 2014 from a distance of 7 km from the comet surface. Seth_01 measures about 220 m across.

Right, top: context image showing fine structure in the comet’s jets as seen from a distance of 28 km from the comet’s surface on 22 November 2014. The image was taken with the OSIRIS wide-angle camera and has a resolution is 2.8 m/pixel. In both images the contrast is deliberately stretched in order to see the details of the activity. The active pits in this study contribute a small fraction of the observed activity.

Left, bottom: how the pits may form through sinkhole collapse. 1. Heat causes subsurface ices to sublimate (blue arrows), forming a cavity (2). When the ceiling becomes too weak to support its own weight, it collapses, creating a deep, circular pit (3, red arrow). Newly exposed material in the pit walls sublimates, accounting for the observed activity (3, blue arrows).

Full story: Comet sinkholes generate jets


Source: ESA

Understanding how stars form from molecular gas

Fig. 1: Eagle Nebula imaged by Hubble Space Telescope.
Credit: NASA, ESA/Hubble and the Hubble Heritage Team (STScI/AURA)
 

Fig. 2: Top: This plot is linking the depletion time and a specific combination of star formation rate (SFR) and stellar surface density. Each data point represents a grid cell of 1kpc x 1kpc size within different structures of the galaxies analysed.

Bottom: The optical image of one of the galaxies in the sample, NGC 5457. Coloured squares show grids cells, with 1 kpc on a side, in the arm (green), interarm (yellow) and bulge (red) regions.



The star formation rate in galaxies varies greatly both across different galaxy types and over galactic time scales. MPA astronomers have been trying to gain insight into how the interstellar medium may change in different galaxies by studying molecular gas in a wide variety of galaxies, ranging from gas-poor, massive ellipticals to strongly star-forming irregulars, and in environments ranging from inner bulges to outer disks. They find that the gas depletion time depends both on the strength of the local gravitational forces and the star formation activity inside the galaxy. 

Molecular clouds are clouds in galaxies consisting predominantly of molecular hydrogen. They are stellar nurseries where the gas reaches high enough densities to form new stars and planetary systems. Molecular clouds are highly complex structures. Figure 1 shows a Hubble Space Telescope image of the Eagle Nebula, a nearby molecular cloud with a highly filamentary and irregular structure. 

In the neighbourhood of our Sun, molecular clouds make up only 1 % of the total volume of the interstellar medium and form stars at modest rates of a few solar masses per year. In the early Universe, however, there is mounting evidence that galaxies contain much more molecular gas and therefore they can form stars at rates up to a thousand times higher than in our Milky Way. The densities and pressures in the interstellar media of these early galaxies are also orders of magnitude higher than in the solar neighbourhood, and it is unlikely that molecular clouds in these systems are the same as the very well-studied Eagle nebula. 

In recent work, the MPA group studied variations in the relation between the local density of molecular gas and newly formed stars. They used this as a diagnostic of changing conditions within the interstellar medium. According to standard theory, molecular clouds exist in a balance between gravitational forces, which work to collapse the cloud, and pressure forces (primarily from the gas), which work to keep the cloud from collapsing. When these forces fall out of balance, such as can happen in a supernova shock wave, the cloud begins to collapse and fragment into smaller and smaller pieces. The smallest of these fragments begin contracting and become proto-stars. 

Gravitational forces vary significantly from one galaxy to the next, as well as in different regions of the same galaxy. At the centre of a giant elliptical galaxy, gravity is much higher than in the outskirts of a small dwarf irregular. Likewise, the incidence of supernova explosions can differ drastically between different galaxies and between different locations within the same galaxy. Variations in the ratio of the density of molecular gas to young stars (commonly referred to as the depletion time of the molecular gas) may thus be expected as a consequence of these changing conditions. 

The main result (see Figure 2) from the MPA group's analysis is that the rate at which molecular gas forms new stars is set BOTH by gravity (as measured by the local surface density of stars in the galaxy) and by the local star formation activity level in the galaxy, which in turn will determine the incidence of supernova-driven shock waves in the interstellar medium. Molecular gas depletion times are shortest in regions where gravity is strong and where the star formation activity is high, particularly in galaxy bulges with gas and ongoing star formation. 

Reaching this conclusion required very careful analysis of a variety of data sets at different wavelengths. In particular, star formation rates derived from the combination of infrared images that trace young stars embedded inside dusty clouds and far-ultraviolet images that trace stars that have migrated outside these clouds, are crucial for pinpointing these relations as accurately as possible. In future, new state-of-the-art interferometric radio telescopes, in particular the Atacama Large Millimeter/submillimeter Array (ALMA), will allow us to understand the detailed structure of molecular clouds in regions of high gravity in much more detail.

Guinevere Kauffmann and Mei-Ling Huang


Publications:

Huang M.-L., Kauffmann G., 2014, MNRAS, 443, 1329
Huang M.-L., Kauffmann G., 2015, MNRAS, 450, 1375



Wednesday, July 01, 2015

Buried in the Heart of a Giant

The colourful star cluster NGC 2367
The star cluster NGC 2367 in the constellation of Canis Major
 
Wide-field view of the sky around the bright star cluster NGC 2367




Videos 

Zooming in on the star cluster NGC 2367
Zooming in on the star cluster NGC 2367

The colourful star cluster NGC 2367
The colourful star cluster NGC 2367



This rich view of an array of colourful stars and gas was captured by the Wide Field Imager (WFI) camera, on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. It shows a young open cluster of stars known as NGC 2367, an infant stellar grouping that lies at the centre of an immense and ancient structure on the margins of the Milky Way.

Discovered from England by the tireless observer Sir William Herschel on 20 November 1784, the bright star cluster NGC 2367 lies about 7000 light-years from Earth in the constellation Canis Major. Having only existed for about five million years, most of its stars are young and hot and shine with an intense blue light. This contrasts wonderfully in this new image with the silky-red glow from the surrounding hydrogen gas.

Open clusters like NGC 2367 are a common sight in spiral galaxies like the Milky Way, and tend to form in their host’s outer regions. On their travels about the galactic centre, they are affected by the gravity of other clusters, as well as by large clouds of gas that they pass close to. Because open clusters are only loosely bound by gravity to begin with, and because they constantly lose mass as some of their gas is pushed away by the radiation of the young hot stars, these disturbances occur often enough to cause the stars to wander off from their siblings, just as the Sun is believed to have done many years ago. An open cluster is generally expected to survive for a few hundred million years before it is completely dispersed.

In the meantime, clusters serve as excellent case studies for stellar evolution. All the constituent stars are born at roughly the same time from the same cloud of material, meaning they can be compared alongside one another with greater ease, allowing their ages to be readily determined and their evolution mapped.

Like many open clusters, NGC 2367 is embedded within an emission nebula, from which its stars were born. The remains show up as wisps and clouds of hydrogen gas, ionised by the ultraviolet radiation being emitted by the hottest stars. What is more unusual is that, as you begin to pan out from the cluster and its nebula, a far more expansive structure is revealed: NGC 2367 and the nebula containing it are thought to be the nucleus of a larger nebula, known as Brand 16, which in turn is only a small part of a huge supershell, known as GS234-02.

The GS234-02 supershell lies towards the outskirts of our galaxy, the Milky Way. It is a vast structure, spanning hundreds of light-years. It began its life when a group of particularly massive stars, producing strong stellar winds, created individual expanding bubbles of hot gas. These neighbouring bubbles eventually merged to form a superbubble, and the short life spans of the stars at its heart meant that they exploded as supernovae at similar times, expanding the superbubble even further, to the point that it merged with other superbubbles, which is when the supershell was formed. The resulting formation ranks as one of the largest possible structures within a galaxy.

This concentrically expanding system, as ancient as it is enormous, provides a wonderful example of the intricate, interrelated structures that are sculpted in galaxies by the lives and deaths of stars.



More Information

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. 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, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.


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Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email:
rhook@eso.org 

Source: ESO