Discovery of a Retrograde or Highly Tilted Extrasolar Planet

The panels show two possibilities for the bizarre orbit of HAT-P-7b. The top panel shows a "polar" orbit in which the planet goes over the north and south poles of the star. The bottom panel shows a "retrograde" orbit in which the planet revolves in the opposite direction as the star's rotation. Astronomers cannot distinguish these two possibilities because the exact orientation of the star's rotation axis is not yet known. Illustrations: Simon Albrecht/MIT

Figure 1

An illustration of the concept of the Rossiter-McLaughlin effect. Each star generally rotates by itself and has an approaching part and a receding part. During a planetary transit, we can see the Rossiter-McLaughlin effect, which is an apparent anomaly of the stellar radial velocity, the star appears to be receding if the transiting planet hides an approaching part and vice versa. We can observe this effect by precise radial velocity measurements. Note that if the planet orbits in a prograde manner, the planet first hides an approaching side and subsequently hides a receding side. Inversely, if the planet orbits in a retrograde manner, the effect occurs in reverse.

Figure 2　

The observational result of the Rossiter-McLaughlin effect on UT May 30, 2008 taken with the Subaru HDS (Narita et al. 2009). This figure shows that the HAT-P-7b first hides a receding part of the HAT-P-7 and subsequently hides an approaching side.

Figure 3

The observational result of the Rossiter-McLaughlin effect on UT July 1, 2009 taken with the Subaru HDS (Winn et al. 2009). This result also indicates a retrograde orbit of HAT-P-7b as well as the previous figure.

Two teams of astronomers have found that extrasolar planet HAT-P-7b, discovered in 2008, has a retrograde or highly tilted orbit. On UT May 30, 2008, a Japanese collaboration led by Norio Narita (National Astronomical Observatory of Japan) used the Subaru Telescope’s High Dispersion Spectrograph (HDS) to observe the HAT-P-7 planetary system, which is about 1000 light years distant from Earth, and found the first evidence of a retrograde orbit of the extrasolar planet HAT-P-7b. On UT July 1, 2009, a US collaboration led by Joshua N. Winn (Massachusetts Institute of Technology) also used the Subaru Telescope’s HDS to independently observe the HAT-P-7 system and likewise concluded that extrasolar planet HAT-P-7b has a retrograde or polar orbit. Both observational results were independently submitted and accepted to scientific journals in August 2009, and were published in October 2009.

The HAT-P-7b is the first planet that indicates a retrograde orbit at the time of publications in scientific journals. Such retrograde or spin-orbit misaligned planets are important for understanding the diversity of planetary systems, and they provide important evidence for assessing current planetary migration models. It is now well known that extrasolar planets have diverse orbits, and recent planetary migration models have predicted the existence of such retrograde or highly tilted extrasolar planets. The Subaru findings provide an important milestone for understanding the orbital evolution of planetary systems.

Extrasolar planets are planets beyond our Solar System. With the advent of large ground-based telescopes and innovative instruments to enhance the flexibility of observations since the 1990s, over 400 extrasolar planets have been discovered since the first one was identified in 1995. The discoveries taught us that orbits of extrasolar planets are very different from those of the planets in the Solar System. For instance, dozens of extrasolar Jovian planets orbit their host stars with a period of a few days ("hot Jupiters"), and many of the extrasolar planets have significant eccentricities ("eccentric planets"). In order to understand the diversity of planetary orbits, many theoretical models for planetary migration have been developed.

Widely held beliefs about planetary system formation have maintained that planetary systems form in rotating protoplanetary disks surrounding protostars. Thus the planetary orbital axis and the stellar spin axis are generally considered to be well aligned, as is true for the planets in the Solar System. However, recent theories have not followed suit. For example, planetary migration models considering gravitational interactions between multiple giant planets ("planet-planet scattering models") or considering Kozai cycles due to a distant companion star ("Kozai migration") predict that a significant fraction of migrated planets have tilted, or even retrograde orbits to the stellar spin axis. Retrograde orbits are those in which the planetary orbit is tilted by over 90 degrees to the stellar spin axis.

A collaboration led by Norio Narita at National Astronomical Observatory of Japan has used the Subaru Telescope to make observations that test such planetary migration models. The team focused on the Rossiter-McLaughlin effect, which is an apparent irregularity in the star’s radial velocity; the star appears to be receding if the transiting planet hides an approaching part and vice versa. By measuring the Rossiter-McLaughlin effect, one can estimate the sky-projected angle between the stellar spin axis and the planetary orbital axis. The Subaru telescope succeeded in detecting the effect in the TrES-1 transiting planetary system in 2007 (a press release at the Subaru website on August 23, 2007), and since then the Subaru Telescope has made observations of several transiting planetary systems. During the observation of the planetary system on UT May 30, 2008, the Japanese team found the first evidence of a retrograde or highly tilted orbit of the HAT-P-7b based on the Rossiter-McLaughlin effect. The result indicates that the planet first hides the receding part of the stellar surface and then the approaching part. The independent observations on UT July 1, 2009 of the US collaboration led by Joshua N. Winn at MIT confirmed these findings (a press release at the MIT website on November 12, 2009).

At this point, however, the migration model for HAT-P-7b has not yet been firmly discriminated. Thus further observations of this system to search for outer massive planets or a binary companion would be interesting. In addition, since the HAT-P-7 system is within the field of view of the Kepler mission, further characterization of this interesting planet HAT-P-7b will be undertaken in the near future.

These studies were published in the Publications of Astronomical Society of Japan Letters (issue published on October 25, 2009) and the Astrophysical Journal Letters (issue publised on October 1, 2009).

REFERENCES:

Norio Narita, Bun'ei Sato, Teruyuki Hirano, Motohide Tamura, 2009 "First Evidence of a Retrograde Orbit of a Transiting Exoplanet HAT-P-7b" Publ. Astron. Soc. Japan, Vol. 61, No. 5, L35-L40.

Joshua N. Winn, John Asher Johnson, Simon Albrecht, Andrew W. Howard, Geoffrey W. Marcy, Ian J. Crossfield, Matthew J. Holman, 2009 "HAT-P-7: A Retrograde or Polar Orbit, and a Third Body" The Astrophysical Journal Letters, Volume 703, Issue 2, pp. L99-L103.

Ticking Stellar Time Bomb Identified

ESO PR Photo 43a/09

The expanding shell

around V445 Puppis

ESO PR Photo 43b/09

Around the nova

V445 Puppis annotated

ESO PR Photo 43c/09

Around the nova V445 Puppis

ESO PR Photo 43d/09

Shell around V445 Puppis

(March 2005)

ESO PR Photo 43e/09

Shell around V445 Puppis

(December 2005)

ESO PR Photo 43f/09

Shell around V445 Puppis

(October 2006)

ESO PR Photo 43g/09

Shell around V445 Puppis

(March 2007)

ESO PR Video 43a/09

The expanding shell

around V445 Puppis

ESO PR Video 43b/09

Artist’s impression of vampire star

Astronomers find prime suspect for a Type Ia supernova

Using ESO’s Very Large Telescope and its ability to obtain images as sharp as if taken from space, astronomers have made the first time-lapse movie of a rather unusual shell ejected by a “vampire star”, which in November 2000 underwent an outburst after gulping down part of its companion’s matter. This enabled astronomers to determine the distance and intrinsic brightness of the outbursting object. It appears that this double star system is a prime candidate to be one of the long-sought progenitors of the exploding stars known as Type Ia supernovae, critical for studies of dark energy.

“One of the major problems in modern astrophysics is the fact that we still do not know exactly what kinds of stellar system explode as a Type Ia supernova,” says Patrick Woudt, from the University of Cape Town and lead author of the paper reporting the results. “As these supernovae play a crucial role in showing that the Universe’s expansion is currently accelerating, pushed by a mysterious dark energy, it is rather embarrassing.”

The astronomers studied the object known as V445 in the constellation of Puppis (“the Stern”) in great detail. V445 Puppis is the first, and so far only, nova showing no evidence at all for hydrogen. It provides the first evidence for an outburst on the surface of a white dwarf [1] dominated by helium. “This is critical, as we know that Type Ia supernovae lack hydrogen,” says co-author Danny Steeghs, from the University of Warwick, UK, “and the companion star in V445 Pup fits this nicely by also lacking hydrogen, instead dumping mainly helium gas onto the white dwarf.”

In November 2000, this system underwent a nova outburst, becoming 250 times brighter than before and ejecting a large quantity of matter into space.

The team of astronomers used the NACO adaptive optics instrument [2] on ESO’s Very Large Telescope (VLT) to obtain very sharp images of V445 Puppis over a time span of two years. The images show a bipolar shell, initially with a very narrow waist, with lobes on each side. Two knots are also seen at both the extreme ends of the shell, which appear to move at about 30 million kilometres per hour. The shell — unlike any previously observed for a nova — is itself moving at about 24 million kilometres per hour. A thick disc of dust, which must have been produced during the last outburst, obscures the two central stars.

“The incredible detail that we can see on such small scales — about hundred milliarcseconds, which is the apparent size of a one euro coin seen from about forty kilometres — is only possible thanks to the adaptive optics technology available on large ground-based telescopes such as ESO’s VLT,” says Steeghs.

A supernova is one way that a star can end its life, exploding in a display of grandiose fireworks. One family of supernovae, called Type Ia supernovae, are of particular interest in cosmology as they can be used as “standard candles” to measure distances in the Universe [3] and so can be used to calibrate the accelerating expansion that is driven by dark energy.

One defining characteristic of Type Ia supernovae is the lack of hydrogen in their spectrum. Yet hydrogen is the most common chemical element in the Universe. Such supernovae most likely arise in systems composed of two stars, one of them being the end product of the life of sun-like stars, or white dwarfs. When such white dwarfs, acting as stellar vampires that suck matter from their companion, become heavier than a given limit, they become unstable and explode [4].

The build-up is not a simple process. As the white dwarf cannibalises its prey, matter accumulates on its surface. If this layer becomes too dense, it becomes unstable and erupts as a nova. These controlled, mini-explosions eject part of the accumulated matter back into space. The crucial question is thus to know whether the white dwarf can manage to gain weight despite the outburst, that is, if some of the matter taken from the companion stays on the white dwarf, so that it will eventually become heavy enough to explode as a supernova.

Combining the NACO images with data obtained with several other telescopes [5] the astronomers could determine the distance of the system — about 25 000 light-years from the Sun — and its intrinsic brightness — over 10 000 times brighter than the Sun. This implies that the vampire white dwarf in this system has a high mass that is near its fatal limit and is still simultaneously being fed by its companion at a high rate. “Whether V445 Puppis will eventually explode as a supernova, or if the current nova outburst has pre-empted that pathway by ejecting too much matter back into space is still unclear,” says Woudt. “But we have here a pretty good suspect for a future Type Ia supernova!”

Notes

[1] White dwarfs represent the evolutionary end product of stars with initial masses up to a few solar masses. A white dwarf is the burnt-out stellar core that is left behind when a star like the Sun sheds its outer layers towards the end of its active life. It is composed essentially of carbon and oxygen. This process normally also leads to the formation of a surrounding planetary nebula.

[2] Adaptive optics is a technique that allows astronomers to obtain an image of an object free from the blurring effect of the atmosphere. See the adaptive optics page at ESO: http://www.eso.org/public/astronomy/technology/adaptive_optics.html

[3] See for example http://www.eso.org/~bleibund/papers/EPN/epn.html

[4] This Chandrasekhar limit, named after the Indian physicist Subrahmanyan Chandrasekhar, is nearly 1.4 times the mass of the Sun. When a white dwarf reaches a mass above this limit, either by sucking matter from a companion or merging with another white dwarf, it will turn itself into a thermonuclear bomb that will burn carbon and oxygen explosively.

[5] The team also used the SOFI instrument on ESO’s New Technology Telescope, the IMACS spectrograph on the 6.5-metre Magellan Baade telescope, and the Infrared Survey Facility and the SIRIUS camera at the Sutherland station of the South African Astronomical Observatory.

More Information

This research was presented in a paper to appear in the 20 November 2009 issue of the Astrophysical Journal, vol. 706, p. 738 (“The expanding bipolar shell of the helium nova V445 Puppis”, by P. A. Woudt et al.).

The team is composed of P. A. Woudt and B. Warner (University of Cape Town, South Africa), D. Steeghs and T. R. Marsh (University of Warwick, UK), M. Karovska and G. H. A. Roelofs (Harvard-Smithsonian Center for Astrophysics, Cambridge MA, USA), P. J. Groot and G. Nelemans (Radboud University Nijmegen, the Netherlands), T. Nagayama (Kyoto University, Japan), D. P. Smits (University of South Africa, South Africa), and T. O’Brien (University of Manchester, UK).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. 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. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Research paper: http://arxiv.org/abs/0910.1069

Contacts

Patrick Woudt
University of Cape Town,
South Africa
Phone: +27 21 650 5830
E-mail: Patrick.Woudt@uct.ac.za

Danny Steeghs
University of Warwick, UK
Phone: +44 (0)2476 573873
Mobile: +44 (0)78 45555979
E-mail: D.T.H.Steeghs@warwick.ac.uk

ESO La Silla - Paranal - ELT Press Officer: Henri Boffin - +49 89 3200 6222 - hboffin@eso.org
ESO Press Officer in Chile: Valeria Foncea - +56 2 463 3123 - vfoncea@eso.org

National contacts for the media: http://www.eso.org/public/outreach/eson/

Close-Up Movie Shows Hidden Details in the Birth of Super-Suns

Artist's conception of the "boiling disk" surrounding the massive young stellar object known as Orion Source I. A disk of hot, ionized gas surrounds the central star, blocking our view. A cool wind of gas is driven from the upper and lower surfaces of the disk (as indicated by the colored arrows) and is sculpted into an hourglass shape by tangled magnetic field lines (shown as thin blue lines). This outflow is lit up by emission from silicon monoxide molecules - emission that has been imaged and tracked by radio astronomers month-to-month. The entire disk and wind are rotating, leading to observable Doppler shifts of the material entrained in the wind; redder colors represent material with a component of motion away from the observer (into the plane of the sky), while bluer colors represent material moving toward the observer (out of the plane of the sky).Credit: Bill Saxton, NRAO/AUI/NSF

This movie shows actual data from the Very Long Baseline Array, which imaged clumps of gas flowing away from the young protostar known as Source I over the course of two years. Gas moving toward us (blueshifted) is colored green or blue, while gas moving away from us (redshifted) is colored yellow, orange and red. The protostar is not visible to the VLBA; its location is marked by a red dot and crosshairs. Credit: L. Matthews (MIT)

Animation (mov)

Cambridge, MA - The constellation of Orion is a hotbed of massive star formation, most prominently in the Great Nebula that sits in Orion's sword. The glowing gas of the Nebula is powered by a group of young massive stars, but behind it is a cluster of younger stars and clumps of gas. Still gathering together under gravity's pull, these gas clumps will eventually ignite into stars.

The youthful cluster cannot be seen with traditional telescopes because of the surrounding gas and dust, but a new high-resolution time-lapse movie reveals the process of massive star formation with radio images a thousand times sharper and more detailed than any previously obtained. The movie shows that massive stars form like their smaller siblings, with disk accretion and magnetic fields playing crucial roles.

The way that massive stars form remains mysterious, in part, because massive stars are rare and tend to spend their youth enshrouded by dust and gas hiding them from view.

"We know how these stars die, but not how they are born," said Lincoln Greenhill, a principal investigator of the study and part of a team comprising scientists from the Harvard-Smithsonian Center for Astrophysics (CfA) and the National Radio Astronomy Observatory (NRAO).

Unlike Hubble and other visible-light telescopes, radio telescopes can penetrate dusty veils around stars. The research astronomers studied a massive young protostar called Source I (pronounced "eye") at radio wavelengths, using the National Science Foundation's Very Long Baseline Array (VLBA) as a powerful "zoom lens."

The VLBA yielded even sharper images than the famous Hubble photos of "proplyds," or protoplanetary disks in Orion. The team observed Source I at monthly intervals over two years and then assembled the individual images into a time-lapse movie.

The VLBA detected thousands of silicon monoxide gas clouds called masers - naturally occurring laser-like beacons often associated with star formation. Some masers were as close to the protostar as Jupiter is to our Sun, which is also a record. Many of the masers existed long enough for their motions to be tracked across the sky and along our line of sight, yielding their 3-d motions through space.

"Source I is the richest source of masers in the Galaxy, that we know of," said Lynn Matthews, lead author of the new work, who is now a researcher at the MIT Haystack Observatory. "Without the masers, we couldn't track the gas motions in such detail so close to this massive star, and would be relatively blind to its formation."

"In astronomy, it's rare to see changes over the course of a human lifetime. With this new movie, we can see changes over just a few months as gas clumps swarm around this young protostar," added Smithsonian astronomer and co-author Ciriaco Goddi.

The resulting movie reveals signs of a rotating accretion disk, where gas is swirling closer and closer to the protostar at the center. It also shows material flowing outward perpendicular to the disk in two large V's - actually the edges of cone-shaped streams of gas. Such outflows foster star formation by carrying angular momentum away from the system.

Intriguingly, the outflow streams appear to curve as they leave the disk. "The bending path of these masers provides key evidence that magnetic fields may be influencing gas motions very close to the protostar," pointed out Claire Chandler of NRAO, a co-principal investigator of the study.

Magnetic field lines are familiar from their effect on iron filings sprinkled around a bar magnet, outlining loops extending from one pole of the magnet to the other. In the case of Source I and other massive protostars, magnetic field lines may extend outward into space, wrapping in a helix that is shaped much like Twizzlers candy. Outflowing gas streams along those field lines.

"Magnetic fields are supposed to be weak and unimportant to the birth process for massive stars," said Matthews. "But masers would not travel along gentle arcs unless they experience some sort of force - probably a magnetic force."

The data don't show whether the magnetic field arises in the star or in the accretion disk. Future observations by the Expanded Very Large Array (E-VLA) and the Atacama Large Millimeter Array (ALMA) may be able to distinguish between competing hypotheses. The team plans to look for other fingerprints of magnetic fields around Source I.

"Our two-year movie is just the beginning," said Smithsonian astronomer and co-principal investigator Elizabeth Humphreys.

The paper describing these findings will appear in the Astrophysical Journal early next year, in January 2010, and it is available online at http://arxiv.org/abs/0911.2473. This material is based upon work supported by the National Science Foundation under Grant No. 0507478.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

Exoplanets Clue to Sun's Curious Chemistry

ESO PR Photo 42a/09

Burning lithium inside a star

A ground-breaking census of 500 stars, 70 of which are known to host planets, has successfully linked the long-standing “lithium mystery” observed in the Sun to the presence of planetary systems. Using ESO’s successful HARPS spectrograph, a team of astronomers has found that Sun-like stars that host planets have destroyed their lithium much more efficiently than “planet-free” stars. This finding does not only shed light on the lack of lithium in our star, but also provides astronomers with a very efficient way of finding stars with planetary systems.

“For almost 10 years we have tried to find out what distinguishes stars with planetary systems from their barren cousins,” says Garik Israelian, lead author of a paper appearing this week in the journal Nature. “We have now found that the amount of lithium in Sun-like stars depends on whether or not they have planets.”

Low levels of this chemical element have been noticed for decades in the Sun, as compared to other solar-like stars, and astronomers have been unable to explain the anomaly. The discovery of a trend among planet-bearing stars provides a natural explanation to this long-standing mystery. “The explanation of this 60 year-long puzzle is for us rather simple,” adds Israelian. “The Sun lacks lithium because it has planets.”

This conclusion is based on the analysis of 500 stars, including 70 planet-hosting stars. Most of these stars were monitored for several years with ESO’s High Accuracy Radial Velocity Planet Searcher. This spectrograph, better known as HARPS, is attached to ESO's 3.6-metre telescope and is the world’s foremost exoplanet hunter. “This is the best possible sample available to date to understand what makes planet-bearing stars unique,” says co-author Michel Mayor.

The astronomers looked in particular at Sun-like stars, almost a quarter of the whole sample. They found that the majority of stars hosting planets possess less than 1% of the amount of lithium shown by most of the other stars. “Like our Sun, these stars have been very efficient at destroying the lithium they inherited at birth,” says team member Nuno Santos. “Using our unique, large sample, we can also prove that the reason for this lithium reduction is not related to any other property of the star, such as its age.”

Unlike most other elements lighter than iron, the light nuclei of lithium, beryllium and boron are not produced in significant amounts in stars. Instead, it is thought that lithium, composed of just three protons and four neutrons, was mainly produced just after the Big Bang, 13.7 billion years ago. Most stars will thus have the same amount of lithium, unless this element has been destroyed inside the star.

This result also provides the astronomers with a new, cost-effective way to search for planetary systems: by checking the amount of lithium present in a star astronomers can decide which stars are worthy of further significant observing efforts.

Now that a link between the presence of planets and curiously low levels of lithium has been established, the physical mechanism behind it has to be investigated. “There are several ways in which a planet can disturb the internal motions of matter in its host star, thereby rearrange the distribution of the various chemical elements and possibly cause the destruction of lithium. It is now up to the theoreticians to figure out which one is the most likely to happen,” concludes Mayor.

More Information

This research was presented in a paper that appears in the 12 November 2009 issue of Nature (Enhanced lithium depletion in Sun-like stars with orbiting planets, by G. Israelian et al.).

The team is composed of Garik Israelian, Elisa Delgado Mena, Carolina Domínguez Cerdeña, and Rafael Rebolo (Instituto de Astrofisíca de Canarias, La Laguna, Tenerife, Spain), Nuno Santos and Sergio Sousa (Centro de Astrofisica, Universidade de Porto, Portugal), Michel Mayor and Stéphane Udry (Observatoire de Genève, Switzerland), and Sofia Randich (INAF, Osservatorio di Arcetri, Firenze, Italy).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. 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. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links

Science paper
More info: Exoplanet Media Kit
Project page of G. Israelian : http://www.iac.es/proyecto/abuntest/framesetwelcome.htm
ESO press release 10/01

Contacts

Garik Israelian
Insitituto de Astrofisica de Canarias, Tenerife, Spain
Phone: +34 922 60 5258
E-mail: gil@iac.es

Nuno Santos, Sergio Sousa
Centro de Astrofisica da Universidade do Porto, Portugal
Phone: +351 226 089 893
E-mail: Nuno.Santos@astro.up.pt, sousasag@astro.up.pt

Michel Mayor, Stéphane Udry
Observatory of Geneva University, Switzerland
Phone: +41 22 379 22 00
Email: Michel.Mayor@obs.unige.ch, Stephane.Udry@obs.unige.ch


ESO La Silla - Paranal - ELT Press Officer: Henri Boffin - +49 89 3200 6222 - hboffin@eso.org
ESO Press Officer in Chile: Valeria Foncea - +56 2 463 3123 - vfoncea@eso.org

National contacts for the media: http://www.eso.org/public/outreach/eson/

Rapid Star Formation Spotted in Infant Galaxies

The Universe’s infant galaxies enjoyed rapid growth spurts forming stars like our sun at a rate of up to 50 stars a year, according to scientists at Durham University.

The findings show that “stellar nurseries” within the first galaxies gave birth to stars at a much more rapid rate than previously expected, the researchers from Durham’s Institute for Computational Cosmology revealed. Their work appears in a paper in the journal Monthly Notices of the Royal Astronomical Society.

The research looked back 12.5 billion years to one of the most distant known galaxies, seen as it appeared about one billion years after the Big Bang.

Using a technique called gravitational lensing – where distant galaxies are magnified using the gravity of a nearby galaxy cluster – the scientists observed the rapid bursts of star formation in the galaxy called MS1358arc.

Within the star-forming regions, new stars were being created at a rate of about 50 stars per year - around 100 times faster than had been previously thought.

The researchers, who say their work represents the most detailed study of a galaxy at such a young age, believe the observed galaxy is typical of others in the early Universe.

They say the galaxy, which measures 6,000 light years across, also has all the characteristics that would allow it to eventually evolve into a galaxy such as our Milky Way, giving an insight into how our sun and galaxy formed.

The Durham researchers based their findings on observations from the Gemini North telescope, based in Hawaii, and NASA’s Hubble and Spitzer Space Telescopes. The research was funded by the Royal Astronomical Society.

Lead author Dr Mark Swinbank, who is the Norman Lockyer Fellow of the Royal Astronomical Society and works in the Institute for Computational Cosmology, at Durham University, said: “The runaway effect in this galaxy suggests it is growing much faster than expected.

“Given the size of the star forming regions, we would expect it to be forming stars at the rate of about one sun per year, but it seems to be much more active than that.

“We think this galaxy is fairly typical of galaxies at this time and we expect that the Milky Way once looked like this as it formed its first stars.

“In effect we are seeing the first generation of stars being born in a galaxy like the Milky Way. This gives unique insight into the birth of our own galaxy.”

The researchers say most of the observed stars eventually exploded as supernovae, spewing debris back into space where it formed into new stars

Dr Swinbank added: “In this respect these stars are the seeds of future star formation in the Universe.”

Royal Astronomical Society President Professor Andy Fabian said: “It is exciting to see such a detailed picture of a very distant galaxy.

“This pioneering work shows what our own galaxy might have looked like when it was a tenth of its present age."

Forwarded from Durham University by:

Dr Robert Massey
Press and Policy Officer
Royal Astronomical Society
Tel: +44 (0)20 7734 3307
Mob: +44 (0)794 124 8035
E-mail: rm@ras.org.uk

CONTACTS

Dr Mark Swinbank
RAS Norman Lockyer Fellow
Institute for Computational Cosmology
Department of Physics
Durham University
Tel: +44 (0)191 334 3786
E-mail: a.m.swinbank@durham.ac.uk

Dr Swinbank is available for interview on Tuesday, November 10, and Wednesday, November 11.

Alternatively please contact

Durham University Media Relations Office
Tel: +44 (0)191 334 6075
E-mail: media.relations@durham.ac.uk

Note to broadcasters: An ISDN broadcast quality line is available via the Media Relations Office on the contact details above. The ISDN number is +44 (0)191 386 2749.

IMAGES

A 300dpi j-peg image showing the distant galaxy MS1358arc is available from Durham University Media Relations Office on request on +44 (0)191 334 6075 or e-mail media.relations@durham.ac.uk

Caption: A Hubble Space Telescope observation showing the red ‘arc’ of the rapid star forming galaxy MS1358arc – seen as it was 12.5 billion years ago. The galaxy is magnified by a factor of 10 by the younger foreground galaxies. (Credit: Dr Johan Richard, Durham University.)

Source Information:

A Spatially Resolved Map of the Kinematics, Star-Formation and Stellar Mass Assembly in a Star-Forming Galaxy at z=4.9, Swinbank, AM, et al, Monthly Notices of the Royal Astronomical Society, 2009, DOI (10.1111/j.1365-2966.2009.15617.x)

A PDF copy of the paper is available on request from Durham University Media Relations Office.

Institute for Computational Cosmology, Durham University: www.icc.dur.ac.uk/
Royal Astronomical Society: www.ras.org.uk/
Gemini Observatory: www.gemini.edu/
Spitzer Space Telescope: www.spitzer.caltech.edu/
Hubble Space Telescope: http://hubblesite.org/

DURHAM UNIVERSITY – A MEMBER OF THE 1994 GROUP

Durham University is a member of the 1994 Group of 19 leading research-intensive universities. The Group was established in 1994 to promote excellence in university research and teaching. Each member undertakes diverse and high-quality research, while ensuring excellent levels of teaching and student experience. www.1994group.ac.uk

ROYAL ASTRONOMICAL SOCIETY

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Swift XMM-Newton Satellites Tune Into a Middleweight Black Hole

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Swift X-ray observations of galaxy NGC 5408 indicate its ultraluminous X-ray source undergoes periodic changes every 115.5 days. This cycle, astronomers suspect, is linked to the orbit of a donor star around a middleweight black hole, as shown in this artist's view. Credit: NASA

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This archival image taken by the Hubble Space Telescope shows the location of NGC 5408's unusually luminous X-ray source (circled). The irregular-type galaxy lies 15.8 million light-years away in the constellation Centaurus. Credit: NASA/ESA/C. Lang, P. Kaaret, A. Mercer (Univ. of Iowa), and S. Corbel (Univ. of Paris)

While astronomers have studied lightweight and heavyweight black holes for decades, the evidence for black holes with intermediate masses has been much harder to come by. Now, astronomers at NASA's Goddard Space Flight Center in Greenbelt, Md., find that an X-ray source in galaxy NGC 5408 represents one of the best cases for a middleweight black hole to date.

"Intermediate-mass black holes contain between 100 and 10,000 times the sun's mass," explained Tod Strohmayer, an astrophysicist at Goddard. "We observe the heavyweight black holes in the centers of galaxies and the lightweight ones orbiting stars in our own galaxy. But finding the 'tweeners' remains a challenge."

Several nearby galaxies contain brilliant objects known as ultraluminous X-ray sources (ULXs). They appear to emit more energy than any known process powered by stars but less energy than the centers of active galaxies, which are known to contain million-solar-mass black holes.

"ULXs are good candidates for intermediate-mass black holes, and the one in galaxy NGC 5408 is especially interesting," said Richard Mushotzky, an astrophysicist at the University of Maryland, College Park. The galaxy lies 15.8 million light-years away in the constellation Centaurus.

Using the European Space Agency's orbiting XMM-Newton observatory, Strohmayer and Mushotzky studied the source -- known as NGC 5408 X-1 -- in 2006 and 2008.

XMM-Newton detected what the astronomers call "quasi-periodic oscillations," a nearly regular "flickering" caused by the pile-up of hot gas deep within the accretion disk that forms around a massive object. The rate of this flickering was about 100 times slower than that seen from stellar-mass black holes. Yet, in X-rays, NGC 5408 X-1 outshines these systems by about the same factor.

Based on the timing of the oscillations and other characteristics of the emission, Strohmayer and Mushotzky conclude that NGC 5408 X-1 contains between 1,000 and 9,000 solar masses. This study appears in the October 1 issue of The Astrophysical Journal.

"For this mass range, a black hole's event horizon -- the part beyond which we cannot see -- is between 3,800 and 34,000 miles across, or less than half of Earth's diameter to about four times its size," said Strohmayer.

If NGC 5408 X-1 is indeed actively gobbling gas to fuel its prodigious X-ray emission, the material likely flows to the black hole from an orbiting star. This is typical for stellar-mass black holes in our galaxy.

Strohmayer next enlisted the help of NASA's Swift satellite to search for subtle variations of X-rays that would signal the orbit of NGC 5408 X-1's donor star. "Swift uniquely provides both the X-ray imaging sensitivity and the scheduling flexibility to enable a search like this," he added. Beginning in April 2008, Swift began turning its X-Ray Telescope toward NGC 5408 X-1 a couple of times a week as part of an on-going campaign.

Swift detects a slight rise and fall of X-rays every 115.5 days. "If this is indeed the orbital period of a stellar companion," Strohmayer said, "then it's likely a giant or supergiant star between three and five times the sun's mass." This study has been accepted for publication in a future issue of The Astrophysical Journal.

The Swift observations cover only about four orbital cycles, so continued observation is needed to confirm the orbital nature of the X-ray modulation.

"Astronomers have been studying NGC 5408 X-1 for a long time because it is one of the best candidates for an intermediate-mass black hole," adds Philip Kaaret at the University of Iowa, who has studied the object at radio wavelengths but is unaffiliated with either study. "These new results probe what is happening close to the black hole and add strong evidence that it is unusually massive."

Related Links: NASA's Swift mission

Francis Reddy
Goddard Space Flight Center

Galactic Center: NASA's Great Observatories Examine the Galactic Center Region

Credit X-ray: NASA/CXC/UMass/D. Wang et al.;
Optical: NASA/ESA/STScI/D.Wang et al.;
IR: NASA/JPL-Caltech/SSC/S.Stolovy

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In celebration of the International Year of Astronomy 2009, NASA's Great Observatories -- the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory -- have collaborated to produce an unprecedented image of the central region of our Milky Way galaxy.

In this spectacular image, observations using infrared light and X-ray light see through the obscuring dust and reveal the intense activity near the galactic core. Note that the center of the galaxy is located within the bright white region to the right of and just below the middle of the image (labeled Sagitarrius A when you roll your mouse over the above composite image). The entire image width covers about one-half a degree, about the same angular width as the full moon.

Each telescope's contribution is presented in a different color:

- Yellow represents the near-infrared observations of Hubble. They outline the energetic regions where stars are being born as well as reveal hundreds of thousands of stars.

- Red represents the infrared observations of Spitzer. The radiation and winds from stars create glowing dust clouds that exhibit complex structures from compact, spherical globules to long, stringy filaments.

- Blue and violet represents the X-ray observations of Chandra. X-rays are emitted by gas heated to millions of degrees by stellar explosions and by outflows from the supermassive black hole in the galaxy's center. The bright blue blob on the left side of the full field image is emission from a double star
system containing either a neutron star or a black hole.

When these views are brought together, this composite image provides one of the most detailed views ever of our galaxy's mysterious core.

Fast Facts for Galactic Center:

Scale: Image is 38 by 14 arcmin
Category: Normal Galaxies & Starburst Galaxies, Milky Way Galaxy
Coordinates: (J2000) RA 17h 45m 36s | Dec -28° 55' 58.8
Constellation: Sagittarius
Observation Date: 03/29/2000 - 07/19/2007
Observation Time: 26 days 3 hours
Obs. ID: 658,944-945, 1561, 2267-2296, 2943, 2951-2954, 3392-3393, 3549, 3663, 3665, 4500, 4683-4684, 5360, 5892, 5950-5954, 6113, 6363, 6639, 6640-6646, 7034-7048, 7345-7346, 7554-7557, 8214, 8459, 8567
Color Code: X-ray (Blue, Purple); Optical (Yellow); IR (Red)
Instrument: ACIS
Distance Estimate: 26,000 light years (8 kiloparsecs)

Rapid supernova could be new class of exploding star

SN 2002bj
Credit:Martin Mobberley

BERKELEY, CA—An unusual supernova rediscovered in seven-year-old data taken at the W. M. Keck Observatory and Lick Observatory may be the first example of a new type of exploding star, possibly in a binary star system where helium flows from one white dwarf onto another and detonates in a thermonuclear explosion.

In a paper first published online Nov. 5 in Science Express, astronomer Dovi Poznanski, of the University of California, Berkeley (UCB) and Lawrence Berkeley National Laboratory (LBNL), and his colleagues describe supernovae SN 2002bj and review the data that suggest it is a new type of stellar explosion.

The supernova was detected in 2002 in the galaxy NGC 1821, in the constellation Lepus, by UC Berkeley astronomer Alex Filippenko’s Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory near San Jose, as well as by amateur astronomers. The exploding star’s spectrum was obtained seven days after its discovery using the Keck I telescope with its Low Resolution Imaging Spectrograph.

The supernova was erroneously classified by the astronomical community as a common Type II supernova and filed away.

In June 2009, Poznanski reanalyzed the spectrum while reviewing data of Type II supernovae, which he wants to use as distance indicators to confirm the accelerating expansion of the Universe. When he carefully examined a high-quality spectrum of SN 2002bj, he realized that the supernova was not a Type II at all, but an unusual kind of supernova more akin to a Type Ia.

According to follow-up images made by KAIT, SN 2002bj disappeared 20 days after its discovery. An image of that area of the sky taken seven days prior to its discovery showed no supernova, so it had brightened and dimmed into obscurity in less than 27 days. Most supernovae brighten and dim over three to four months.

“This is the fastest evolving supernova we have ever seen,” said Poznanski, a UC Berkeley post-doctoral fellow who recently joined LBNL’s Computational Cosmology Center. “It was three to four times faster than a standard supernova.”

This rapid drop, coupled with the supernova’s faintness, the strong signature of helium in the spectrum of the explosion, the absence of hydrogen, and the possible presence of vanadium – an element never previously identified in supernova spectra – points toward helium detonation on a white dwarf.

“We think this may well be a new physical explosion mechanism, not just a minor variation of ones already known,” said Filippenko, a coauthor on the study. “This supernova is qualitatively different from the complete disruption of a white dwarf, known as a Type Ia supernova, or the collapse of an iron core and rebound of the surrounding material, so-called ‘core-collapse supernovae.’”

Co-author Joshua Bloom, of UCB, added that astronomers have seen great diversity in those two main supernova mechanisms, “but even within that diversity, observationally, there is a limited range of variation spectrally and in how events evolve in time,” he said. “This object (SN 2002bj) falls outside that range.”

Based on the available images and spectra SN 2002bj, Poznanski and graduate student Ryan Chornock – now a post-doctoral fellow at Harvard University – determined that the theory involving AM Canum Venaticorum (AM CVn) binary systems best matches the data. In this theory, the system is composed to two white dwarfs, one of which is primarily made of helium that is being slowly pulled by gravity onto its companion. White dwarfs are the remnants of stars that burned their hydrogen down to carbon and oxygen or, in some particular cases, to helium.

According to models of AM CVn systems, when enough helium has accumulated on the surface of the primary white dwarf, an explosion will occur that can power a faint and rapidly rising thermonuclear supernova. The event is now called a .Ia (point one A) supernova, because it is one-tenth as bright for one-tenth the time as a Type Ia supernova.

Filippenko added, however, that this explosion is nothing like a regular Type Ia explosion because the white dwarf survives the detonation of the helium shell. In fact, it has similarities to both a nova and a supernova. Novas occur when matter – primarily hydrogen – falls onto a star and accumulates in a shell that can flare up as brief thermonuclear explosions. SN 2002bj is, however, a “super” nova because it generated about 1,000 times the energy of a standard nova, he said.

The past few years have yielded a bonanza of weird supernovae, Filippenko said. “A lot of us who have studied supernovae for several decades are amazed at the quality and quantity of data coming in recently, showing interesting new subclasses or even strange new physical classes of supernovae,” he said. “It whets my appetite for what else we might find out there.”

The W. M. Keck Observatory operates two 10-meter optical/infrared telescopes on the summit of Mauna Kea on the island of Hawai’i. The twin telescopes feature a suite of advanced instrumentation including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and a world-leading laser guide star adaptive optics system. The Observatory is a scientific partnership of the California Institute of Technology, the University of California and NASA. For more information please call 808.881.3827 or visit http://www.keckobservatory.org.

“Dropouts” pinpoint earliest galaxies

False color image of the Z7 galaxy

This is a composite of false color images of the galaxies found at the early epoch around 800 million years after the Big Bang. The upper left panel presents the galaxy confirmed in the 787 million year old universe. These galaxies are in the Subaru Deep Field. (These images are created by M. Ouchi et al., which are the reproduction of Figure 3 in the Astrophysical Journal December 2009 issue.)

Plot of ionization history

This plot shows galaxies' ionizing photon production rate as a function of cosmic age. Red bar indicates the team’s measurements and associated uncertainties at around 800 million years. Black points denote the previous measurements made at the universe older than about 1 billion years. The dark-grey area represents the epoch and rate that nearly comes short of photons to ionize the universe. The red bar falls on the boarder with the dark area. (This plot is created by M. Ouchi et al. It is a reproduction of Figure 10 in the Astrophysical Journal December 2009 issue.)

Cosmic star-formation history

Cosmic star-formation history from today to the epoch of 800 million years after the Big Bang is shown in this plot. The red bar is the star-formation rate density at around 800 million years, obtained by the present study. Black circles and dotted line are measurements and the best-fit model in the more recent universe, between today and 1 billion years post Big Bang. (This plot is created by M. Ouchi et al. It is s reproduction of Figure 9 in the Astrophysical Journal December 2009 issue.)

Pasadena, CA—Astronomers, conducting the broadest survey to date of galaxies from about 800 million years after the Big Bang, have found 22 early galaxies and confirmed the age of one by its characteristic hydrogen signature at 787 million years post Big Bang. The finding is the first age-confirmation of a so-called dropout galaxy at that distant time and pinpoints when an era called the reionization epoch likely began. The research will be published in a December issue of the Astrophysical Journal.

With recent technological advancements, such as the Wide-Field Camera 3 on the Hubble Space Telescope, there has been an explosion of research of the reionization period, the farthest back in time that astronomers can observe. The Big Bang, 13.7 billion years ago, created a hot, murky universe. Some 400,000 years later, temperatures cooled, electrons and protons joined to form neutral hydrogen, and the murk cleared. Some time before 1 billion years after the Big Bang, neutral hydrogen began to form stars in the first galaxies, which radiated energy and changed the hydrogen back to being ionized. Although not the thick plasma soup of the earlier period just after the Big Bang, this star formation started the reionization epoch. Astronomers know that this era ended about 1 billion years after the Big Bang, but when it began has eluded them and intrigued researchers like lead author Masami Ouchi of the Carnegie Observatories.

The U.S. and Japanese team led by Ouchi used a technique for finding these extremely distant galaxies. “We look for ‘dropout’ galaxies,” explained Ouchi. “We use progressively redder filters that reveal increasing wavelengths of light and watch which galaxies disappear from or ‘dropout’ of images made using those filters. Older, more distant galaxies ‘dropout’ of progressively redder filters and the specific wavelengths can tell us the galaxies’ distance and age. What makes this study different is that we surveyed an area that is over 100 times larger than previous ones and, as a result, had a larger sample of early galaxies (22) than past surveys. Plus, we were able to confirm one galaxy’s age,” he continued. “Since all the galaxies were found using the same dropout technique, they are likely to be the same age.”

Ouchi’s team was able to conduct such a large survey because they used a custom-made, super-red filter and other unique technological advancements in red sensitivity on the wide-field camera of the 8.3-meter Subaru Telescope. They made their observations from 2006 to 2009 in the Subaru Deep Field and Great Observatories Origins Deep Survey North field. They then compared their observations with data gathered in other studies.

Astronomers have wondered whether the universe underwent reionization instantaneously or gradually over time, but more importantly, they have tried to isolate when the universe began reionization. Galaxy density and brightness measurements are key to calculating star-formation rates, which tell a lot about what happened when. The astronomers looked at star-formation rates and the rate at which hydrogen was ionized.

Using data from their study and others, they determined that the star-formation rates were dramatically lower from 800 million years to about one billion years after the Big Bang, than thereafter. Accordingly, they calculated that the rate of ionization would be very slow during this early time, because of this low star-formation rate.

“We were really surprised that the rate of ionization seems so low, which would constitute a contradiction with the claim of NASA’s WMAP satellite. It concluded that reionization started no later than 600 million years after the Big Bang,” remarked Ouchi. “We think this riddle might be explained by more efficient ionizing photon production rates in early galaxies. The formation of massive stars may have been much more vigorous then than in today’s galaxies. Fewer, massive stars produce more ionizing photons than many smaller stars,” he explained.

The work was funded by the Carnegie Institution. The research is based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the Hubble Space Telescope, operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555; the Spitzer Telescope, managed by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

Gamma-ray sources guide astronomers to pulsars

The rapidly rotating ultradense remnant of a massive star, a pulsar emits jets of radiation that sweep across space like a lighthouse beam, as shown in this illustration. For the first time, gamma-ray observations have provided clues to radio astronomers about where to find millisecond pulsars. Credit: NASA

Fermi Telescope observations provide candidates to check for radio emissions
By Ron Cowen

WASHINGTON — Energetic gamma rays are providing astronomers with a new way to hunt those hard-to-find whirling dervishes known as pulsars.

“We usually have to look over the whole sky” to find pulsars, said Scott Ransom of the National Radio Astronomy Observatory in Charlottesville, Va. “Now we can use the gamma-ray point sources as guides, telling us exactly where to look.”

Ultradense, collapsed remnants of massive stars, pulsars rotate up to hundreds of times a second and emit beacons of light that sweep across the sky like lighthouse beams. Pulsars are not only predicted to be key sources of gravitational waves — the subtle ripples in spacetime predicted by Einstein’s theory of general relativity — but their clockwork pulses can be used to detect those waves in surrounding space.

Although researchers have calculated that the Milky Way galaxy contains tens of thousands of the fastest spinning pulsars, known as millisecond pulsars, radio telescopes have found only about 100. Because these celestial bodies can reside anywhere in the galaxy, searching for millisecond pulsars was like looking for the proverbial needle in a haystack, requiring radio surveys of the entire sky, noted Ransom, who presented his new work November 2 during the 2009 Fermi Symposium.

Last year, pulsar hunters got some encouraging news. Researchers using the Fermi Gamma-ray Space Telescope demonstrated that many millisecond pulsars emit gamma rays. However, many pulsars emit so few high-energy gamma rays — only 300 to 1,000 over an entire year — that it has been difficult to use the gamma rays to identify the period of many of these pulsars (or even to clearly identify if any of these rapid rotators are the source of the gamma rays).

But Ransom and colleagues calculated that a significant number of the unidentified gamma-ray sources found by Fermi might turn out to be pulsars. So the researchers recently aimed a giant radio dish, the Green Bank Telescope in West Virginia, at four of these sources and found that three were indeed radio-emitting millisecond pulsars, Ransom reported.

“For the first time, gamma-ray observations are guiding radio observations,” commented Fermi researcher Peter Michelson of Stanford University in Palo Alto, Calif.

The gamma-ray technique may soon reveal dozens of previously unknown pulsars, Ransom estimated, including radio-bright pulsars whose radio emissions could be clocked to reveal the presence of gravitational waves (SN: 6/6/09, p. 14).

Hubble Image Showcases Star Birth in M83, the Southern Pinwheel

Credit: NASA, ESA, R. O'Connell (University of Virginia),

the WFC3 Science Oversight Committee, and ESO

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The spectacular new camera installed on NASA's Hubble Space Telescope during Servicing Mission 4 in May has delivered the most detailed view of star birth in the graceful, curving arms of the nearby spiral galaxy M83.

Nicknamed the Southern Pinwheel, M83 is undergoing more rapid star formation than our own Milky Way galaxy, especially in its nucleus. The sharp "eye" of the Wide Field Camera 3 (WFC3) has captured hundreds of young star clusters, ancient swarms of globular star clusters, and hundreds of thousands of individual stars, mostly blue supergiants and red supergiants.

The image at right is Hubble's close-up view of the myriad stars near the galaxy's core, the bright whitish region at far right. An image of the entire galaxy, taken by the European Southern Observatory's Wide Field Imager on the ESO/MPG 2.2-meter telescope at La Silla, Chile, is shown at left. The white box outlines Hubble's view.

WFC3's broad wavelength range, from ultraviolet to near-infrared, reveals stars at different stages of evolution, allowing astronomers to dissect the galaxy's star-formation history.

The image reveals in unprecedented detail the current rapid rate of star birth in this famous "grand design" spiral galaxy. The newest generations of stars are forming largely in clusters on the edges of the dark dust lanes, the backbone of the spiral arms. These fledgling stars, only a few million years old, are bursting out of their dusty cocoons and producing bubbles of reddish glowing hydrogen gas.

The excavated regions give a colorful "Swiss cheese" appearance to the spiral arm. Gradually, the young stars' fierce winds (streams of charged particles) blow away the gas, revealing bright blue star clusters. These stars are about 1 million to 10 million years old. The older populations of stars are not as blue.

A bar of stars, gas, and dust slicing across the core of the galaxy may be instigating most of the star birth in the galaxy's core. The bar funnels material to the galaxy's center, where the most active star formation is taking place. The brightest star clusters reside along an arc near the core.

The remains of about 60 supernova blasts, the deaths of massive stars, can be seen in the image, five times more than known previously in this region. WFC3 identified the remnants of exploded stars. By studying these remnants, astronomers can better understand the nature of the progenitor stars, which are responsible for the creation and dispersal of most of the galaxy's heavy elements.

M83, located in the Southern Hemisphere, is often compared to M51, dubbed the Whirlpool galaxy, in the Northern Hemisphere. Located 15 million light-years away in the constellation Hydra, M83 is two times closer to Earth than M51.

Credit for Hubble image: NASA, ESA, R. O'Connell (University of Virginia), B. Whitmore (Space Telescope Science Institute), M. Dopita (Australian National University), and the Wide Field Camera 3 Science Oversight Committee

For additional information, contact:

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

Robert O'Connell
University of Virginia, Charlottesville, Va.
434-924-7494
rwo@virginia.edu

Brad Whitmore
Space Telescope Science Institute, Baltimore, Md.
410-338-4474
whitmore@stsci.edu

Object Name: M83
Image Type: Astronomical

Credit for Hubble Image: NASA, ESA, R. O'Connell (University of Virginia), B. Whitmore (Space Telescope Science Institute), M. Dopita (Australian National University), and the Wide Field Camera 3 Science Oversight Committee

Credit for Ground-based Image: European Southern Observatory