Saturday, August 01, 2015

Silhouettes of Early Galaxies Reveal Few Seeds for New Stars

Artist’s impression of the gas surrounding a young galaxy in the distant universe. The gas, shown as red streams on the left, is actually invisible, and the starlight from the galaxy is too faint for astronomers to see directly. Instead, the gas is seen in silhouette against a bright, background quasar. Molecules in the gas imprint a shadow, or absorption line, onto the quasar light at a very specific color, as seen on the right, and astronomers can detect this shadow. Image credits: ESO/L. Calçada/ESA/AOES Medialab, Swinburne Astronomy Productions - Hi-res image 5.10 MB JPEG


An international team of astronomers has discovered that gas around young galaxies is almost barren, devoid of the seeds from which new stars are thought to form—molecules of hydrogen.

Without starlight to see them directly, the team, which includes Dr. Regina Jorgenson of the Institute for Astronomy at the University of Hawaii at Manoa—observed the young galaxies’ outskirts in silhouette.

They searched for telltale signs of hydrogen molecules absorbing the light from background objects called quasars—supermassive black holes sucking in surrounding material—that glow very brightly.

“Previous experiments led us to expect molecules in about 10 of the 90 young galaxies we observed, but we

found just one case,” said Associate Professor Michael Murphy from Swinburne University of Technology in
Australia. He co-led the study with Jorgenson.

Astronomers believe that stars begin to form in cold gas that is rich in molecules. The team observed galaxies at a time when the Universe was most actively forming stars, about 12 billion years ago.

“This is a little mystery. This is when most stars are born, and we think this gas forms stars eventually, but it lacks the key ingredient—molecules—to do so,” Murphy said.

The team believes that location and time are the key.

“The gas we observe in silhouette probably lies too far from the galaxies to form stars,” Jorgenson said.

“It’s got lots of potential, but it hasn’t had time to fall into the richer, denser parts of the galaxies which might be better stellar nurseries.”

The researchers made new observations of more than 50 quasars for this study using the 6.5-meter Magellan telescopes in Chile.

It was conducted by researchers from the University of Hawaii at Manoa, Swinburne University of Technology, the University of Cambridge and the University of Arizona.


Contacts:

Dr. Regina Jorgenson
raj@ifa.hawaii.edu
Dr. Roy Gal
cell: +1 301-728-8637

rgal@ifa.hawaii.edu


Ms. Louise Good
Media Contact
+1 808-956-9403
good@ifa.hawaii.edu




Record Precision Achieved in Mass Map of Galaxy Cluster Discovered from Maunakea

Figure 1: This image from the Hubble Space Telescope shows the galaxy cluster MACSJ0416.1-2403, one of six being studied by the Hubble Frontier Fields program, which analyzes the mass distribution in these huge clusters and uses them, combined with a process known as gravitational lensing, to peer even deeper into the distant universe. A team of researchers used almost 200 images of distant galaxies, whose light has been bent and magnified by this huge cluster, combined with new Hubble data, to measure the total mass of this cluster more precisely than ever before.Credit: ESA/Hubble, NASA, HST Frontier Fields. Acknowledgement: Mathilde Jauzac (Durham University, UK and Astrophysics & Cosmology Research Unit, South Africa) and Jean-Paul Kneib (École Polytechnique Fédérale de Lausanne, Switzerland). (32.7 Mb TIFF or 10.5 Mb JPEG )

Figure 2: This image shows the galaxy MACSJ0416.1-2403, one of six clusters targeted by the Hubble Frontier Fields program. The varying intensity of the blue haze in this image is a mass map created by using new Hubble observations combined with the magnifying power of a process known as gravitational lensing. Strong lensing gives a much more precise indication of the mass at the cluster’s core, while weak lensing provides valuable information about the mass surrounding the cluster core. Credit: ESA/Hubble, NASA, HST Frontier Fields. Acknowledgement: Mathilde Jauzac (Durham University, UK and Astrophysics & Cosmology Research Unit, South Africa) and Jean-Paul Kneib (École Polytechnique Fédérale de Lausanne, Switzerland). (23.4 Mb TIFF or10.0 Mb JPEG)


An international team of astronomers, including Dr. Harald Ebeling of the University of Hawaii at Manoa Institute for Astronomy, has used the Hubble Space Telescope to map the mass within a galaxy cluster, originally discovered with Maunakea telescopes, more precisely than ever before.

Clusters of galaxies are the most massive objects in the universe, comprising hundreds to thousands of galaxies and also enormous amounts of invisible dark matter. They grow through collisions in which smaller clusters merge into ever more massive systems, a process that can temporarily lead to highly complex mass distributions.

Ebeling specializes in finding the rarest, most extreme clusters that are the most rewarding targets for detailed studies of the formation and evolution of cosmic structure. One of the clusters discovered by Ebeling’s team in the course of the Massive Cluster Survey (MACS), which used several telescopes on Maunakea, goes by the unpoetic name of MACSJ0416.1-2403.

It was found to be so massive that the cluster was selected for extremely deep observations with the Hubble Space Telescope as part of the Frontier Fields program. The resulting Hubble data show the galaxy distribution within the cluster in stunning detail (Figure 1). The new, ultra-deep observations also reveal a multitude of distorted images of galaxies that are in fact far behind the cluster, bent and often appearing multiple times within the Hubble image of MACSJ0416 due to an effect called gravitational lensing, in which the mass of a foreground object magnifies and distorts more distant objects.  

Gravitational lensing by mass concentrations in space comes in two varieties: so-called “strong lensing,” which creates the highly elongated, almost linear images of distant background galaxies visible near the center of the cluster (as predicted by Einstein’s theory of relativity), and “weak lensing,” pioneered by IfA’s Nick Kaiser in the 1990s, which causes much less perceptible, faint, statistical distortions of hundreds of background galaxies viewed at larger distances from the cluster core.

The spectacular images collected of MACSJ0416 during the Frontier Fields program were recently analyzed by members of the team led by Mathilde Jauzac (Durham University, UK. and Astrophysics & Cosmology Research Unit, South Africa). They used both strong- and weak-lensing techniques to infer the cluster mass distribution that creates the many lensing features identified in these data.  

Their meticulous search for even the faintest gravitationally lensed images was unprecedentedly successful, resulting in the identification of four times as many lensed background galaxies as were previously known in this system. The result is a mass map of MACSJ0416 that is more precise than any ever derived for any galaxy cluster, showing the highly elongated distribution of dark matter in this merging cluster in great detail and over an enormous range of scales (Figure 2). The study also established MACSJ0416 as a huge cluster indeed, with a measured mass of 160 trillion times the mass of the sun.   

“Our analysis of the Frontier Fields data demonstrates impressively how detailed studies of the extremely massive clusters found by MACS can advance our understanding not only of the complexity of cluster formation but in fact of the distant universe behind these powerful gravitational lenses,” explains Ebeling.

Further investigations of MACSJ0416 are underway, combining the Frontier Fields images with deep X-ray observations of the hot gas within the cluster and with spectroscopic redshifts of the cluster galaxies, measured by Ebeling as part of the follow-up work conducted by the MACS team using Maunakea facilities. Primary goal: to deduce the merger history of this extreme cluster by establishing its three-dimensional geometry and the trajectories of the clusters involved in the collision.

The results of the study will be published in Monthly Notices of the Royal Astronomical Society in July 2014. 

Additional information can be found in this press release by the European Space Agency: http://www.spacetelescope.org/news/heic1416/.



Contacts:

Dr. Harald Ebeling
ebeling@ifa.hawaii.edu

Dr. Roy Gal
+1 808-956-6235
cell: +1 301-728-8637
rgal@ifa.hawaii.edu

Ms. Louise Good
Media Contact
+1 808-956-9403
good@ifa.hawaii.edu

Source: Institute for Astronomy - Universityof Hawaii

Friday, July 31, 2015

Gemini Observatory / University of Hawai‘i, Institute for Astronomy

Artist's rendering of a possible exoplanetary system with a gas-giant planet orbiting close to his parent star which is more massive than our sun. 
Artwork by Lynette Cook
Credit: Gemini Observatory/AURAFull Resolution TIFF (6MB) | Full Resolution JPEG (2MB) | Medium Resolution JPEG (296KB)


Gemini Observatory’s Planet-Finding Campaign finds that, around many types of stars, distant gas-giant planets are rare and prefer to cling close to their parent stars. The impact on theories of planetary formation could be significant.

Finding extrasolar planets has become so commonplace that it seems astronomers merely have to look up and another world is discovered. However, results from Gemini Observatory’s recently completed Planet-Finding Campaign – the deepest, most extensive direct imaging survey to date – show the vast outlying orbital space around many types of stars is largely devoid of gas-giant planets, which apparently tend to dwell close to their parent stars.

“It seems that gas-giant exoplanets are like clinging offspring,” says Michael Liu of the University of Hawaii’s Institute for Astronomy and leader of the Gemini Planet-Finding Campaign. “Most tend to shun orbital zones far from their parents. In our search, we could have found gas giants beyond orbital distances corresponding to Uranus and Neptune in our own Solar System, but we didn’t find any.” The Campaign was conducted at the Gemini South telescope in Chile, with funding support for the team from the National Science Foundation and NASA. The Campaign’s results, Liu says, will help scientists better understand how gas-giant planets form, as the orbital distances of planets are a key signature that astronomers use to test exoplanet formation theories.

Eric Nielsen of the University of Hawaii, who leads a new paper about the Campaign’s search for planets around stars more massive than the Sun, adds that the findings have implications beyond the specific stars imaged by the team. "The two largest planets in our Solar System, Jupiter and Saturn, are huddled close to our Sun, within 10 times the distance between the Earth and Sun,” he points out. “We found that this lack of gas-giant planets in more distant orbits is typical for nearby stars over a wide range of masses."

Two additional papers from the Campaign will be published soon and reveal similar tendencies around other classes of stars. However, not all gas-giant exoplanets snuggle so close to home. In 2008, astronomers using the Gemini North telescope and W.M. Keck Observatory on Hawaii’s Mauna Kea took the first-ever direct images of a family of planets around the star HR 8799, finding gas-giant planets at large orbital separations (about 25-70 times the Earth-Sun distance). This discovery came after examining only a few stars, suggesting such large-separation gas giants could be common. The latest Gemini results, from a much more extensive imaging search, show that gas-giant planets at such distances are in fact uncommon.

Liu sums up the situation this way: “We’ve known for nearly 20 years that gas-giant planets exist around other stars, at least orbiting close-in. Thanks to leaps in direct imaging methods, we can now learn how far away planets can typically reside. The answer is that they usually avoid significant areas of real estate around their host stars. The early findings, like HR 8799, probably skewed our perceptions.”

The team’s second new paper explores systems where dust disks around young stars show holes, which astronomers have long suspected are cleared by the gravitational force of orbiting planets. “It makes sense that where you see debris cleared away that a planet would be responsible, but we did not know what types of planets might be causing this. It appears that instead of massive planets, smaller planets that we can’t detect directly could be responsible,” said Zahed Wahhaj of the European Southern Observatory and lead author on the survey’s paper on dusty disk stars. Finally, the third new paper from the team looks at the very youngest stars close to Earth. “A younger system should have brighter, easier to detect planets,” according to the lead author Beth Biller of the Max Planck Institute for Astronomy.

“Around other stars, NASA's Kepler telescope has shown that planets larger than the Earth and within the orbit of Mercury are plentiful,” explains Biller. “The NICI Campaign demonstrates that gas-giant planets beyond the distance of the orbit of Neptune are rare.” The soon-to-be-delivered Gemini Planet Imager will begin to bridge this gap likely revealing, for the first time, how common giant planets are in orbits similar to the gas-giant planets of our own Solar System.

The observations for the Campaign were obtained with the Gemini instrument known as NICI, the Near-Infrared Coronagraphic Imager, which was the first instrument for an 8-10 meter-class telescope designed specifically for finding faint companions around bright stars. NICI was built by Doug Toomey (Mauna Kea Infrared), Christ Ftaclas, and Mark Chun (University of Hawai‘i), with funding from NASA.

The first two papers from the Campaign have been accepted for publication in The Astrophysical Journal (Nielsen et al. and Wahhaj et al.), and the third paper (Biller et al.) will be published later this summer.

The NICI Campaign team is composed of PI Michael Liu, co-PI Mark Chun (University of Hawaii), co-PI Laird Close (University of Arizona), Doug Toomey (Mauna Kea Infrared), Christ Ftaclas (University of Hawaii), Zahed Wahhaj (European Southern Observatory), Beth Biller (Max Planck Institute for Astronomy), Eric Nielsen (University of Hawaii), Evgenya Shkolnik (DTM, Carnegie Institution of Washington), Adam Burrows (Princeton University), Neill Reid (Space Telescope Science Institute), Niranjan Thatte, Matthias Tecza, Fraser Clarke (University of Oxford), Jane Gregorio Hetem, Elisabete De Gouveia Dal Pino (University of Sao Paolo), Silvia Alencar (University of Minas Gerais), Pawel Artymowicz (University of Toronto), Doug Lin (University of California Santa Cruz), Shigeru Ida (Tokyo Institute of Technology), Alan Boss (DTM, Carnegie Institution of Washington), and Mark Kuchner (NASA Goddard), Tom Hayward and Markus Hartung (Gemini Observatory), Jared Males, and Andy Skemer (University of Arizona).


Media Contacts:



  • Peter Michaud
    Gemini Observatory
    Hilo, HI 96720
    Office: +1 (808) 974-2510
    Cell: +1 (808) 936-6643

    pmichaud@gemini.edu

  • Roy Gal
    Institute for Astronomy
    University of Hawaii at Manoa
    Honolulu, HI 96822
    Office: +1 (808) 956-6235

    rgal@ifa.hawaii.edu

Science Contacts:



  • Michael Liu
    Institute for Astronomy
    University of Hawaii at Manoa
    Honolulu, HI 96822
    Office: +1 (808) 956-6666

    mliu@ifa.hawaii.edu

  • Eric Nielsen
    Institute for Astronomy
    University of Hawaii at Manoa
    Honolulu, HI 96822
    Office: +1 (808) 956-9841
    Cell: 408 394-4582

    enielsen@ifa.hawaii.edu



The long goodbye

Credit: ESA/Hubble & NASA
Acknowledgement: M. Novak


A dying star’s final moments are captured in this image from the NASA/ESA Hubble Space Telescope. The death throes of this star may only last mere moments on a cosmological timescale, but this star’s demise is still quite lengthy by our standards, lasting tens of thousands of years!

The star’s agony has culminated in a wonderful planetary nebula known as NGC 6565, a cloud of gas that was ejected from the star after strong stellar winds pushed the star’s outer layers away into space. Once enough material was ejected, the star’s luminous core was exposed and it began to produce ultraviolet radiation, exciting the surrounding gas to varying degrees and causing it to radiate in an attractive array of colours. These same colours can be seen in the famous and impressive Ring Nebula (heic1310), a prominent example of a nebula like this one.

Planetary nebulae are illuminated for around 10 000 years before the central star begins to cool and shrink to become a white dwarf. When this happens, the star’s light drastically diminishes and ceases to excite the surrounding gas, so the nebula fades from view.

A version of this image was entered into the Hubble’s Hidden Treasures basic image competition by contestant Matej Novak.


Source: ESA/Hubble - Space Telescope

Thursday, July 30, 2015

Identification of Exoplanet Host Star OGLE-2005-BLG-169 (Artist's Illustration)

Identification of Exoplanet Host Star OGLE-2005-BLG-169 (Artist's Illustration)
This graphic illustrates how a star can magnify and brighten the light of a background star when it passes in front of the distant star. If the foreground star has planets, then the planets may also magnify the light of the background star, but for a much shorter period of time than their host star. Astronomers use this method, called gravitational microlensing, to identify planets.  Credit: NASA, ESA, and A. Feild (STScI)


NASA's Hubble Space Telescope and the W. M. Keck Observatory in Hawaii have made independent confirmations of an exoplanet orbiting far from its central star. The planet was discovered through a technique called gravitational microlensing.

This finding opens a new piece of discovery space in the extrasolar planet hunt: to uncover planets as far from their central stars as Jupiter and Saturn are from our sun. The Hubble and Keck Observatory results will appear in two papers in the July 30 edition of The Astrophysical Journal.

The large majority of exoplanets cataloged so far are very close to their host stars because several current planet-hunting techniques favor finding planets in short-period orbits. But this is not the case with the microlensing technique, which can find more distant and colder planets in long-period orbits that other methods cannot detect.

Microlensing occurs when a foreground star amplifies the light of a background star that momentarily aligns with it. If the foreground star has planets, then the planets may also amplify the light of the background star, but for a much shorter period of time than their host star. The exact timing and amount of light amplification can reveal clues to the nature of the foreground star and its accompanying planets.

The system, cataloged as OGLE-2005-BLG-169, was discovered in 2005 by the Optical Gravitational Lensing Experiment (OGLE), the Microlensing Follow-Up Network (MicroFUN), and members of the Microlensing Observations in Astrophysics (MOA) collaborations — groups that search for extrasolar planets through gravitational microlensing.

Without conclusively identifying and characterizing the foreground star, however, astronomers have had a difficult time determining the properties of the accompanying planet. Using Hubble and the Keck Observatory, two teams of astronomers have now found that the system consists of a Uranus-sized planet orbiting about 370 million miles from its parent star, slightly less than the distance between Jupiter and the sun. The host star, however, is about 70 percent as massive as our sun.

"These chance alignments are rare, occurring only about once every 1 million years for a given planet, so it was thought that a very long wait would be required before the planetary microlensing signal could be confirmed," said David Bennett of the University of Notre Dame, Indiana, the lead of the team that analyzed the Hubble data. "Fortunately, the planetary signal predicts how fast the apparent positions of the background star and planetary host star will separate, and our observations have confirmed this prediction. The Hubble and Keck Observatory data, therefore, provide the first confirmation of a planetary microlensing signal."

In fact, microlensing is such a powerful tool that it can uncover planets whose host stars cannot be seen by most telescopes. "It is remarkable that we can detect planets orbiting unseen stars, but we'd really like to know something about the stars that these planets orbit," explained Virginie Batista of the Institut d'Astrophysique de Paris, France, leader of the Keck Observatory analysis. "The Keck and Hubble telescopes allow us to detect these faint planetary host stars and determine their properties."

Planets are small and faint compared to their host stars; only a few have been observed directly outside our solar system. Astronomers often rely on two indirect techniques to hunt for extrasolar planets. The first method detects planets by the subtle gravitational tug they give to their host stars. In another method, astronomers watch for small dips in the amount of light from a star as a planet passes in front of it.

Both of these techniques work best when the planets are either extremely massive or when they orbit very close to their parent stars. In these cases, astronomers can reliably determine their short orbital periods, ranging from hours to days to a couple years.

But to fully understand the architecture of distant planetary systems, astronomers must map the entire distribution of planets around a star. Astronomers, therefore, need to look farther away from the star-from about the distance of Jupiter is from our sun, and beyond.

"It's important to understand how these systems compare with our solar system," said team member Jay Anderson of the Space Telescope Science Institute in Baltimore, Maryland. "So we need a complete census of planets in these systems. Gravitational microlensing is critical in helping astronomers gain insights into planetary formation theories."

The planet in the OGLE system is probably an example of a "failed-Jupiter" planet, an object that begins to form a Jupiter-like core of rock and ice weighing around 10 Earth masses, but it doesn't grow fast enough to accrete a significant mass of hydrogen and helium. So it ends up with a mass more than 20 times smaller than that of Jupiter. "Failed-Jupiter planets, like OGLE-2005-BLG-169Lb, are predicted to be more common than Jupiters, especially around stars less massive than the sun, according to the preferred theory of planet formation. So this type of planet is thought to be quite common," Bennett said.

Microlensing takes advantage of the random motion of stars, which are generally too small to be noticed without precise measurements. If one star, however, passes nearly precisely in front of a farther background star, the gravity of the foreground star acts like a giant lens, magnifying the light from the background star.

A planetary companion around the foreground star can produce a variation in the brightening of the background star. This brightening fluctuation can reveal the planet, which can be too faint, in some cases, to be seen by telescopes. The duration of an entire microlensing event is several months, while the variation in brightening due to a planet lasts a few hours to a couple of days.

The initial microlensing data of OGLE-2005-BLG-169 had indicated a combined system of foreground and background stars plus a planet. But due to the blurring effects of our atmosphere, a number of unrelated stars are also blended with the foreground and background stars in the very crowded star field in the direction of our galaxy's center.

The sharp Hubble and Keck Observatory images allowed the research teams to separate out the background source star from its neighbors in the very crowded star field in the direction of our galaxy's center. Although the Hubble images were taken 6.5 years after the lensing event, the source and lens star were still so close together on the sky that their images merged into what looked like an elongated stellar image.

Astronomers can measure the brightness of both the source and planetary host stars from the elongated image. When combined with the information from the microlensing light curve, the lens brightness reveals the masses and orbital separation of the planet and its host star, as well as the distance of the planetary system from Earth. The foreground and background stars were observed in several different colors with Hubble's Wide Field Camera 3 (WFC3), allowing independent confirmations of the mass and distance determinations.

The observations, taken with the Near Infrared Camera 2 (NIRC2) on the Keck 2 telescope more than eight years after the microlensing event, provided a precise measurement of the foreground and background stars' relative motion. "It is the first time we were able to completely resolve the source star and the lensing star after a microlensing event. This enabled us to discriminate between two models that fit the data of the microlensing light curve," Batista said.

The Hubble and Keck Observatory data are providing proof of concept for the primary method of exoplanet detection that will be used by NASA's planned, space-based Wide-Field Infrared Survey Telescope (WFIRST), which will allow astronomers to determine the masses of planets found with microlensing. 

WFIRST will have Hubble's sharpness to search for exoplanets using the microlensing technique. The telescope will be able to observe foreground, planetary host stars approaching the background source stars prior to the microlensing events, and receding from the background source stars after the microlensing events.

"WFIRST will make measurements like we have made for OGLE-2005-BLG-169 for virtually all the planetary microlensing events it observes. We'll know the masses and distances for the thousands of planets discovered by WFIRST," Bennett explained.


Contact:

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

David Bennett
University of Notre Dame, Notre Dame, Indiana
574-315-6621
bennett@nd.edu

Jean-Phillipe Beaulieu
Institut d'Astrophysique de Paris, Paris, France
011-33-6-0398-7311
beaulieu@iap.fr

Source: HubbleSite

Stormy seas in Sagittarius

New Hubble view of the Lagoon Nebula

 
PR Image heic1517b
Wide-field view of the Lagoon Nebula (ground-based image)

Giant 'Twisters' in the Lagoon Nebula


Videos

Zooming in on the Lagoon Nebula
Zooming in on the Lagoon Nebula

Panning across the Lagoon Nebula
Panning across the Lagoon Nebula


Some of the most breathtaking views in the Universe are created by nebulae — hot, glowing clouds of gas. This new NASA/ESA Hubble Space Telescope image shows the centre of the Lagoon Nebula, an object with a deceptively tranquil name. The region is filled with intense winds from hot stars, churning funnels of gas, and energetic star formation, all embedded within an intricate haze of gas and pitch-dark dust.

Nebulae are often named based on their key characteristics — particularly beautiful examples include the Ring Nebula (heic1310), the Horsehead Nebula (heic1307) and the Butterfly Nebula (heic0910). This new NASA/ESA Hubble Space Telescope image shows the centre of the Lagoon Nebula, otherwise known as Messier 8, in the constellation of Sagittarius (The Archer).

The inspiration for this nebula’s name may not be immediately obvious — this is because the image captures only the very heart of the nebula. The Lagoon Nebula’s name becomes much clearer in a wider field view (opo0417i) when the broad, lagoon-shaped dust lane that crosses the glowing gas of the nebula can be made out.

Another clear difference between this new image and others is that this image combines both infrared and optical light rather than being purely optical(heic1015). Infrared light cuts through thick, obscuring patches of dust and gas, revealing the more intricate structures underneath and producing a completely different landscape [1].
However, even in visible light, the tranquil name remains misleading as the region is packed full of violent phenomena.

The bright star embedded in dark clouds at the centre of this image is known as Herschel 36. This star is responsible for sculpting the surrounding cloud, stripping away material and influencing its shape. Herschel 36 is the main source of ionising radiation [2] for this part of the Lagoon Nebula.

This central part of the Lagoon Nebula contains two main structures of gas and dust connected by wispy twisters, visible in the middle third of this image (opo9638). These features are quite similar to their namesakes on Earth — they are thought to be wrapped up into their funnel-like shapes by temperature differences between the hot surface and cold interior of the clouds. The nebula is also actively forming new stars, and energetic winds from these newborns may contribute to creating the twisters.

This image combines images taken using optical and infrared light gathered by Hubble’s Wide Field Planetary Camera 2.


Notes

[1] Another particularly good example of this effect is shown in Hubble’s image of the Horsehead Nebula (heic1307).

[2] The ionising radiation here is ultraviolet light. This light knocks electrons loose from within atoms to create charged particles called ions.


Note for editors

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


More information

Image credit: NASA, ESA, J. Trauger (Jet Propulson Laboratory)


Links

Contacts

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



Brown Dwarfs, Stars Share Formation Process, New Study Indicates


Artist's conception of a very young, still-forming brown dwarf, with a disk of material orbiting it, and jets of material ejected outward from the poles of the disk. 
Credit: Bill Saxton, NRAO/AUI/NSF


Astronomers using the Karl G. Jansky Very Large Array (VLA) have discovered jets of material ejected by still-forming young brown dwarfs. The discovery is the first direct evidence that brown dwarfs, intermediate in mass between stars and planets, are produced by a scaled-down version of the same process that produces stars.

The astronomers studied a sample of still-forming brown dwarfs in a star-forming region some 450 light-years from Earth in the constellation Taurus, and found that four of them have the type of jets emitted by more-massive stars during their formation. The jets were detected by radio observations with the VLA. The scientists also observed the brown dwarfs with the Spitzer and Herschel space telescopes to confirm their status as very young objects.

"This is the first time that such jets have been found coming from brown dwarfs at such an early stage of their formation, and shows that they form in a way similar to that of stars," said Oscar Morata, of the Institute of Astronomy and Astrophysics of the Academia Sinica in Taiwan. "These are the lowest-mass objects that seem to form the same way as stars," he added.

Brown dwarfs are less massive than stars, but more massive than giant planets such as Jupiter. They have insufficient mass to produce the temperatures and pressures at their cores necessary to trigger the thermonuclear reactions that power "normal" stars. Theorists suggested in the 1960s that such objects should exist, but the first unambiguous discovery of one did not come until 1994.

A key question has been whether brown dwarfs form like stars or like planets. Stars form when a giant cloud of gas and dust in interstellar space collapses gravitationally, accumulating mass. A disk of orbiting material forms around the young star, and eventually planets form from the material in that disk. In the early stages of star formation, jets of material are propelled outward from the poles of the disk. No such jets mark planet formation, however.

Previous evidence strongly suggested that brown dwarfs shared the same formation mechanism as their larger siblings, but detecting the telltale jets is an important confirmation. Based on this discovery, "We conclude that the formation of brown dwarfs is a scaled-down version of the process that forms larger stars," Morata said.

Morata led an international team of astronomers with members from Asia, Europe, and Latin America. They reported their findings in the Astrophysical Journal.

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


Contact: 

Dave Finley, Public Information Officer
(575) 835-7302
dfinley@nrao.edu



Wednesday, July 29, 2015

First Detection of Lithium from an Exploding Star

Nova Centauri 2013

 
PR Image eso1531b
Nova Centauri 2013 seen from La Silla

The location of Nova Centauri 2013

The sky around the location of Nova Centauri 2013

The Milky Way and Nova Centauri 2013



Videos
 
Zooming in on Nova Centauri 2013
Zooming in on Nova Centauri 2013


The chemical element lithium has been found for the first time in material ejected by a nova. Observations of Nova Centauri 2013 made using telescopes at ESO’s La Silla Observatory, and near Santiago in Chile, help to explain the mystery of why many young stars seem to have more of this chemical element than expected. This new finding fills in a long-missing piece in the puzzle representing our galaxy’s chemical evolution, and is a big step forward for astronomers trying to understand the amounts of different chemical elements in stars in the Milky Way.

The light chemical element lithium is one of the few elements that is predicted to have been created by the Big Bang, 13.8 billion years ago. But understanding the amounts of lithium observed in stars around us today in the Universe has given astronomers headaches. Older stars have less lithium than expected [1], and some younger ones up to ten times more [2].

Since the 1970s, astronomers have speculated that much of the extra lithium found in young stars may have come from novae — stellar explosions that expel material into the space between the stars, where it contributes to the material that builds the next stellar generation. But careful study of several novae has yielded no clear result up to now.

A team led by Luca Izzo (Sapienza University of Rome, and ICRANet, Pescara, Italy) has now used the FEROS instrument on the MPG/ESO 2.2-metre telescope at the La Silla Observatory, as well the PUCHEROS spectrograph on the ESO 0.5-metre telescope at the Observatory of the Pontificia Universidad Catolica de Chile in Santa Martina near Santiago, to study the nova Nova Centauri 2013 (V1369 Centauri). This star exploded in the southern skies close to the bright star Beta Centauri in December 2013 and was the brightest nova so far this century — easily visible to the naked eye [3].

The very detailed new data revealed the clear signature of lithium being expelled at two million kilometres per hour from the nova [4]. This is the first detection of the element ejected from a nova system to date.

Co-author Massimo Della Valle (INAF–Osservatorio Astronomico di Capodimonte, Naples, and ICRANet, Pescara, Italy) explains the significance of this finding: “It is a very important step forward. If we imagine the history of the chemical evolution of the Milky Way as a big jigsaw, then lithium from novae was one of the most important and puzzling missing pieces. In addition, any model of the Big Bang can be questioned until the lithium conundrum is understood.”

The mass of ejected lithium in Nova Centauri 2013 is estimated to be tiny (less than a billionth of the mass of the Sun), but, as there have been many billions of novae in the history of the Milky Way, this is enough to explain the observed and unexpectedly large amounts of lithium in our galaxy.

Authors Luca Pasquini (ESO, Garching, Germany) and Massimo Della Valle have been looking for evidence of lithium in novae for more than a quarter of a century. This is the satisfying conclusion to a long search for them. And for the younger lead scientist there is a different kind of thrill:

"It is very exciting,” says Luca Izzo, “to find something that was predicted before I was born and then first observed on my birthday in 2013!”




Notes 

[1] The lack of lithium in older stars is a long-standing puzzle. Results on this topic include these press releases: eso1428, eso1235 and eso1132.


[2] More precisely, the terms “younger” and “older” are used to refer to what astronomers call Population I and Population II stars. The Population I category includes the Sun; these stars are rich in heavier chemical elements and form the disc of the Milky Way. Population II stars are older, with a low heavy-element content, and are found in the Milky Way Bulge and Halo, and globular star clusters. Stars in the “younger” Population I class can still be several billion years old!

[3] These comparatively small telescopes, equipped with suitable spectrographs, are powerful tools for this kind of research. Even in the era of extremely large telescopes smaller telescopes dedicated to specific tasks can remain very valuable.

[4] This high velocity, from the nova towards the Earth, means that the wavelength of the line in the absorption in the spectrum due to the presence of lithium is significantly shifted towards the blue end of the spectrum.



More information

This research was presented in a paper entitled “Early optical spectra of Nova V1369 Cen show presence of lithium”, by L. Izzo et al., published online in the Astrophysical Journal Letters.

The team is composed of Luca Izzo (Sapienza University of Rome, and ICRANet, Pescara, Italy), Massimo Della Valle (INAF–Osservatorio Astronomico di Capodimonte, Naples; ICRANet, Pescara, Italy), Elena Mason (INAF–Osservatorio Astronomico di Trieste, Trieste, Italy), Francesca Matteucci (Universitá di Trieste, Trieste, Italy), Donatella Romano (INAF–Osservatorio Astronomico di Bologna, Bologna, Italy), Luca Pasquini (ESO, Garching bei Munchen, Germany), Leonardo Vanzi (Department of Electrical Engineering and Center of Astro Engineering, PUC-Chile, Santiago, Chile), Andres Jordan (Institute of Astrophysics and Center of Astro Engineering, PUC-Chile, Santiago, Chile), José Miguel Fernandez (Institute of Astrophysics, PUC-Chile, Santiago, Chile), Paz Bluhm (Institute of Astrophysics, PUC-Chile, Santiago, Chile), Rafael Brahm (Institute of Astrophysics, PUC-Chile, Santiago, Chile), Nestor Espinoza (Institute of Astrophysics, PUC-Chile, Santiago, Chile) and Robert Williams (STScI, Baltimore, Maryland, USA).


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”.



Links 



Contacts 

Luca Izzo
Sapienza University of Rome/ICRANet
Pescara, Italy
Email:
luca.izzo@gmail.com

Massimo Della Valle
INAF–Osservatorio Astronomico di Capodimonte
Naples, Italy
Email:
dellavalle@na.astro.it

Luca Pasquini
ESO
Garching bei München, Germany
Tel: +49 89 3200 6792
Email:
lpasquin@eso.org

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

What happens when Cosmic Giants meet Galactic Dwarfs?

Cosmic Giants Meet Galactic Dwarfs in GAMA

 A still from the animation available on Dropbox


When two different sized galaxies smash together, the larger galaxy stops the smaller one making new stars, according to a study of more than 20,000 merging galaxies.

The research, published today, also found that when two galaxies of the same size collide, both galaxies produce stars at a much faster rate.

Astrophysicist Luke Davies, from The University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR), says our nearest major galactic neighbour, Andromeda, is hurtling on a collision course with the Milky Way at about 400,000 kilometres per hour.

“Don’t panic yet, the two won’t smash into each other for another four billion years or so,” he says.

“But investigating such cosmic collisions lets us better understand how galaxies grow and evolve.”

Previously, astronomers thought that when two galaxies smash into each other their gas clouds—where stars are born—get churned up and seed the birth of new stars much faster than if they remained separate.

However Dr Davies’ research, using the Galaxy and Mass Assembly (GAMA) survey observed using the Anglo-Australian Telescope in regional New South Wales, suggests this idea is too simplistic.

He says whether a galaxy forms stars more rapidly in a collision, or forms any new stars at all, depends on if it is the big guy or the little guy in this galactic car crash.

“When two galaxies of similar mass collide, they both increase their stellar birth rate,” Dr Davies says.

“However when one galaxy significantly outweighs the other, we have found that star formation rates are affected for both, just in different ways."

“The more massive galaxy begins rapidly forming new stars, whereas the smaller galaxy suddenly struggles to make any at all."

“This might be because the bigger galaxy strips away its smaller companion’s gas, leaving it without star-forming fuel or because it stops the smaller galaxy obtaining the new gas required to form more stars.”

The study was released today in the journal Monthly Notices of the Royal Astronomical Society, published by Oxford University Press.

So what will happen in four billion years to the Milky Way and Andromeda?

Dr Davies says the pair are like “cosmic tanks”—both relatively large and with similar mass.

“As they get closer together they will begin to affect each other’s star formation, and will continue to do so until they eventually merge to become a new galaxy, which some call ‘Milkdromeda’,” he says.


Further information:
ICRAR is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia.

Original publication details:

‘Galaxy and Mass Assembly (GAMA): the effect of close interactions on star formation in galaxies’ in the Monthly Notices of the Royal Astronomical Society. Published online on 13/7/2015 at: http://mnras.oxfordjournals.org/lookup/doi/10.1093/mnras/stv1241


Imagens and Animation:

All images and an animation are available in various resolutions on Dropbox.


Contacts:

Dr Luke Davies
ICRAR – UWA (Perth, GMT +8:00)
Ph: +61 8 6488 7750
M: +61 466 277 672
E:
luke.davies@icrar.org

Pete Wheeler
Media Contact, ICRAR (Perth, GMT +8:00)
Ph: +61 8 6488 7758
M: +61 423 982 018
E:
pete.wheeler@icrar.org

UWA Media Office
Ph: +61 8 6488 7977



Tuesday, July 28, 2015

NOAO: Hiding in Plain Sight: Undergraduates Discover the Densest Galaxies Known

Fig 1: Two ultra-dense galaxies (insets) have been discovered orbiting larger host galaxies. The compact systems are thought to be the remnants of once normal galaxies that were swallowed by the host, a process that removed the fluffy outer parts of the systems, leaving the dense centers behind. Image credit: A. Romanowsky (SJSU), Subaru, Hubble Legacy Archive

Fig 2: Artist's depiction of the night sky as seen from a planet at the heart of an ultracompact galaxy. More than a million stars are visible with the naked eye, in contrast to the few thousand visible from Earth. Image credit: NASA, ESA, G. Bacon (STScI) and P. van Dokkum (Yale University) 

Fig 3. Reconstructed spectrum of light from the ultracompact galaxies M59-UCD3, as seen by the SOAR telescope (top) and M85-HCC1, as seen by the Sloan Digital Sky Survey (bottom). Dark bands are the fingerprints of atoms and molecules in the atmospheres of the stars in the galaxy. These bands reveal the compositions and ages of the stars as well as the velocities of the galaxies. 


Fig 4. Computer animated movie showing the formation of an ultra-dense galaxy: the giant host galaxy disrupts the smaller galaxy, removing its fluffy outer parts, and the dense center is left behind. The animation then zooms in to a possible embedded planet and supermassive black hole. Click for the full version. Credit: M. Sandoval, A. Romanowsky (SJSU).


Two undergraduates at San José State University have discovered two galaxies that are the densest known. Similar to ordinary globular star clusters but a hundred to a thousand times brighter, the new systems have properties intermediate in size and luminosity between galaxies and star clusters.

The first system discovered by the investigators, M59-UCD3, has a width two hundred times smaller than our own Milky Way Galaxy and a stellar density 10,000 times larger than that in the neighborhood of the Sun. For an observer in the core of M59-UCD3, the night sky would be a dazzling display, lit up by a million stars. The stellar density of the second system, M85-HCC1, is higher still: about a million times that of the Solar neighborhood. Both systems belong to the new class of galaxies known as ultracompact dwarfs (UCDs).

The study, led by undergraduates Michael Sandoval and Richard Vo, used imaging data from the Sloan Digital Sky Survey, the Subaru Telescope, and Hubble Space Telescope, as well as spectroscopy from the Goodman Spectrograph on the Southern Astrophysical Research Telescope (SOAR), located on the Cerro Tololo Inter-American Observatory site. The National Optical Astronomy Observatory (NOAO) is a SOAR partner. The SOAR spectrum was used to show that M59-UCD3 is associated with a larger host galaxy, M59, and to measure the age and elemental abundances of the galaxy’s stars.

“Ultracompact stellar systems like these are easy to find once you know what to look for. However, they were overlooked for decades because no one imagined such objects existed: they were hiding in plain sight”, said Richard Vo. “When we discovered one UCD serendipitously, we realized there must be others, and we set out to find them.” 

The students were motivated by the idea that all it takes to initiate a discovery is a good idea, archival data, and dedication. The last element was critical, because the students worked on the project on their own time. Aaron Romanowsky, the faculty mentor and coauthor on the study, explained, “The combination of these elements and the use of national facilities for follow up spectroscopy is a great way to engage undergraduates in frontline astronomical research, especially for teaching universities like San José State that lack large research budgets and their own astronomical facilities.”

The nature and origins of UCDs are mysterious – are they the remnant nuclei of tidally stripped dwarf galaxies, merged stellar super-clusters, or genuine compact dwarf galaxies formed in the smallest peaks of primordial dark matter fluctuations? 

Michael Sandoval favors the tidally stripped hypothesis. “One of the best clues is that some UCDs host overweight supermassive black holes. This suggests that UCDs were originally much bigger galaxies with normal supermassive black holes, whose fluffy outer parts were stripped away, leaving their dense centers behind. This is plausible because the known UCDs are found near massive galaxies that could have done the stripping.” 

An additional line of evidence is the high abundance of heavy elements such as iron in UCDs. Because large galaxies are more efficient factories to make these metals, a high metal content may indicate that the galaxy used to be much larger.

To test this hypothesis, the team will investigate the motions of stars in the center of M59-UCD3 to look for a supermassive black hole. They are also on the hunt for more UCDs, to understand how commonly they occur and how diverse they are.


Reference:

“Hiding in plain sight: record-breaking compact stellar systems in the Sloan Digital Sky Survey,” Michael A. Sandoval, Richard P. Vo, Aaron J. Romanowsky et al. 2015, Astrophysical Journal Letters, 808, L32. (Preprint: http://arxiv.org/abs/1506.08828)

NOAO is operated by Association of Universities for Research in Astronomy Inc. (AURA) under a cooperative agreement with the National Science Foundation.


Science Contact

Dr. Aaron Romanowsky
Department of Physics and Astronomy
San José State University
One Washington Square
San Jose, CA 95192 USA
408-924-5225
E-mail: aaron.romanowsky@sjsu.edu


Born-again planetary nebula

Born-again planetary nebula
Copyright: ESA/XMM-Newton/J.A. Toalá et al. 2015


Beneath the vivid hues of this eye-shaped cloud, named Abell 78, a tale of stellar life and death is unfolding. At the centre of the nebula, a dying star – not unlike our Sun – which shed its outer layers on its way to oblivion has, for a brief period of time, come back to echo its past glory.

Releasing their outer shells is the usual fate for any star with a mass of 0.8–8 times that of the Sun. Having exhausted the nuclear fuel in their cores after burning for billions of years, these stars collapse to become dense, hot white dwarf stars. Around them, the ejected material strikes the ambient gas and dust, creating beautiful clouds known as ‘planetary nebulas’. This curious name was adopted by 18th-century astronomers who discovered these ‘puffing’ stars and thought their round shape similar to that of planets.

However, the resurgence to life seen in this image is an exceptional event for a planetary nebula. Only a handful of such born-again stars have been discovered, and here the intricate shape of the cloud’s glowing material gives away its turbulent history.

Although nuclear burning of hydrogen and helium had ceased in the core of the dying star, causing it to collapse under its own weight and its envelope to expand into a bubble, some of the star’s outer layers became so dense that fusion of helium resumed there.

The renewed nuclear activity triggered another, much faster wind, blowing more material away. The interplay between old and new outflows has shaped the cloud’s complex structure, including the radial filaments that can be seen streaming from the collapsing star at the centre.

The interaction between slow and fast winds gusting in the environment of Abell 78 heated the gas to over a million degrees, making it shine brightly in X-rays. Astronomers detected this hot gas with ESA’s XMM-Newton space observatory, revealing striking similarities with another born-again planetary nebula, Abell 30.

This three-colour image combines X-ray data collected in 2013 by XMM-Newton (blue) with optical observations obtained using two special filters that reveal the glow of oxygen (green) and helium (red). The optical data were gathered in 2014 with the Andalusian Faint Object Spectrograph and Camera at the Nordic Optical Telescope on La Palma, in the Canary Islands. A study of the X-ray emission from Abell 78 is presented in a paper by J.A. Toalá et al. 2015.


Source: ESA

Monday, July 27, 2015

Finding O2

An infrared image of the Orion Nebula; the circled area shows the region where shocks and emission from molecular oxygen are found. 
Credit: ESA/NASA/JPL-Caltech


Oxygen is the third most abundant element in the universe (after hydrogen and helium) and of course it is important: all known life forms require liquid water and its oxygen content. For over thirty years, astronomers have been searching for molecular oxygen, O­2, as part of an accounting of cosmic oxygen atoms. Despite early predictions that O­2 should be abundant in the molecular clouds that form new stars and planetary systems, it is virtually absent. Only two locations have convincing O­2 detections, a region of shocks near the Orion Nebula, and a cloud in the constellation of Ophiuchus. The theory is clearly wrong. What is not clear is whether O­2 is missing (with dramatic implications for its abundance and the chemistry of molecular clouds), is in some less detectable form (perhaps frozen onto dust grains), or has been taken up to form water, carbon monoxide, or other oxygen-bearing molecules.

The launch of the Herschel Space Observatory enabled much more sensitive searches for O­2, and prompted updated chemical modeling for molecular clouds and their oxygen. CfA astronomer Gary Melnick and his colleague improved the models to take into account the role of ultraviolet radiation in modifying the chemical and physical conditions in shocks. Their goal was to explain the strength and proportions of the line emission in Orion, and to understand what made the Orion environment so special.

The scientists report that when UV illuminates the region of a shock, the width and temperature of the shocked region changes, and enhances the O­2 in two ways: by knocking oxygen off dust grains and breaking apart some molecules, thus increasing the number of free atoms before the shock, and by breaking apart water in the post-shock gas so that more O­2 can form. The new model also successfully resolves the outstanding puzzle about its limited detection, finding that the detectability is very sensitive to the size and geometry of the emitting region. The paper provides the first self-consistent treatment of preshock, shock, and postshock regions under the influence of UV fields, and explains why O2 detections are so rare.

Reference(s):


"O2 Emission toward Orion H2 Peak 1 and the Role of FUV-illuminated C-shocks," Gary J. Melnick and Michael J. Kaufman, ApJ 806, 227, 2015.



Treasure hunting in archive data reveals clues about black holes’ diet

These plots show two SDSS spectra of the object; the different luminosities as a function of wavelength between the two epochs are clearly visible. In particular, the red dashed vertical lines show the hydrogen Balmer lines which dramatically change their shape: in the red spectrum they are much broader, which provides a "fingerprint" signature of the accretion onto a central black hole. Credit: © SDSS/MPE.

A snapshot image from a computer simulation of a star disrupted by a supermassive black hole. The red-orange plumes show the debris of the star after its passage near the black hole (located close to the bottom left corner of the image). About half of the disrupted star moves in elliptical orbits around the black hole and forms an accretion disc which eventually shines brightly in optical and X-ray wavelengths. Credit: J. Guillochon (Harvard University) and E. Ramirez-Ruiz (University of California).


Using archival data from the Sloan Digital Sky Survey, and the XMM-Newton and Chandra X-ray telescopes, a team of astronomers have discovered a gigantic black hole, which is probably destroying and devouring a massive star in its vicinity. With a mass of 100 million times more than our Sun, this is the largest black hole caught in this act so far. The results of this study are published in a paper in the journal Monthly Notices of the Royal Astronomical Society.

Andrea Merloni and members of his team, from the Max-Planck Institute for Extraterrestrial Physics (MPE) in Garching, near Munich, were exploring the huge archive of the Sloan Digital Sky Survey (SDSS) in preparation for a future X-ray satellite mission. The SDSS has been observing a large fraction of the night sky with its optical telescope. In addition, spectra (where light is dispersed across wavelengths, allowing astronomers to deduce properties like composition and temperature) have been taken of distant galaxies and black holes.

For a variety of reasons, the spectra of some objects were taken more than once. And when the team was looking at one of the objects with multiple spectra, they were struck by an extraordinary change in one of the objects under study, with the catalogue number SDSS J0159+0033, a galaxy in the constellation of Cetus. The huge distance to the galaxy means that we see it as it was 3.5 billion years ago.

“Usually distant galaxies do not change significantly over an astronomer’s lifetime, i.e. on a timescale of years or decades,” explains Andrea Merloni, “but this one showed a dramatic variation of its spectrum, as if the central black hole had switched on and off.”

This happened between 1998 and 2005, but nobody had noticed the odd behaviour of this galaxy until late last year, when two groups of scientists preparing the next (fourth) generation of SDSS surveys independently stumbled across these data.

Luckily enough, the two flagship X-ray observatories, the ESA-led XMM-Newton and the NASA-led Chandra took snapshots of the same area of the sky close in time to the peak of the flare, and again about ten years later. This gave the astronomers unique information about the high-energy emission that reveals how material is processed in the immediate vicinity of the central black hole.

Gigantic black holes are at home in the nuclei of large galaxies all around us. Most astronomers believe that they grew to the enormous sizes that we can observe today by feeding mostly on interstellar gas from their surroundings, which is unable to escape the immense gravitational pull. Such a process takes place over a very long time (tens to hundreds of millions of years), and is capable of turning a small black hole created in the explosion of a heavy star into the super-heavyweight monsters that lurk at the centre of galaxies.

However, galaxies also contain a huge number of stars. Some unlucky ones may happen to pass too close to the central black hole, where they are destroyed and eventually swallowed by the black hole. If this is compact enough, the strong, tidal gravitational forces tear the star apart in a spectacular way. Subsequently bits and pieces swirl into the black hole and thus produce huge flares of radiation that can be as luminous as all of the rest of the stars in the host galaxy for a period of a few months to a year. These rare events are called Tidal Disruption Flares (TDF).

Merloni and his collaborators quite quickly realised that 'their' flare matched almost perfectly all the expectations of this model. Moreover, because of the serendipitous nature of the discovery, they realised that this was an even more peculiar system than those which had been found through active searches until now. With an estimated mass of 100 million solar masses, this is the biggest black hole caught in the act of star-tearing so far.

However, the sheer size of the system is not the only intriguing aspect of this particular flare; it is also the first one for which scientists can assume with some degree of certainty that the black hole was on a more standard 'gas diet' very recently (a few tens of thousands of years). This is an important clue to finding out which sort of food black holes mostly live on.


"Louis Pasteur said: 'Chance favours the prepared mind' - but in our case, nobody was really prepared," marvels Merloni. "We could have discovered this unique object already ten years ago, but people did not know where to look. It is quite common in astronomy that progress in our understanding of the cosmos is helped by serendipitous discoveries. And now we have a better idea of how to find more such events, and future instruments will greatly expand our reach."

This computer simulation of the disruption of a star by a black hole shows the formation of an accretion disk of stellar material spiralling into the black hole. This sequence shows an early stage in the formation of the disk. The stellar material is coloured according to its temperature, with red being colder and purple hotter. Credit: J. Guillochon and E. Ramirez Ruiz


In less than two years’ time a new powerful X-ray telescope eROSITA, which is currently being built at MPE, will be put into orbit on the Russian-German SRG satellite. It will scan the entire sky with the right cadence and sensitivity needed to discover hundreds of new tidal disruption flares. Big optical telescopes are also being designed and built with the goal of monitoring the variable sky, and will greatly contribute to solving the mystery of black hole eating habits. Astronomers will have to be prepared to catch these dramatic last acts of a star's life. But however prepared they’ll be, the sky will be full of new surprises.



Media contact

Dr Hannelore Hämmerle
Pressesprecherin
Max-Planck-Institut für extraterrestrische Physik
Garching
Germany
Tel: +49 (0)89 30000 3980
pr@mpe.mpg.de

Science contact

Dr Andrea Merloni
Max-Planck-Institut für extraterrestrische Physik
Garching
Germany
Tel: +49 (0)89 30000-3893
am@mpe.mpg.de



Futher information
  • The new work appears in "A tidal disruption flare in a massive galaxy? Implications for the fuelling mechanisms of nuclear black holes", A. Merloni, T. Dwelly, M. Salvato, A. Georgakakis, J. Greiner, M. Krumpe, K. Nandra, G. Ponti, A. Rau, Monthly Notices of the Royal Astronomical Society, Oxford University Press.
  • The other group, who independently discovered the strange light curve of this object, was Stephanie Lamassa (Yale) and her collaborators. They were the fastest to alert the community about this object, but did not explore the stellar disruption interpretation for this event.
  • Tidal Disruption Flares are very rare, with perhaps one occurring every few tens of thousands of year in any given galaxy. In addition, because they do not last very long, they are very hard to find. Only about twenty of them have been studied so far, but with the advent of larger telescopes designed to survey large areas of the sky in a short time, more and more dedicated searches are being carried out, and the pace of discovery is rapidly increasing. 




Notes for editors


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