Credits: NASA/ISAS/DSS/A. Simionescu et al.; inset: NASA/CXC/A. Fabian et al.
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The Japanese Suzaku X-ray telescope has just taken a close look at the Perseus galaxy cluster, and revealed it’s got a bit of a spare tire.
Suzaku explored faint X-ray emission of hot gas across two swaths of the Perseus Galaxy Cluster. The resulting images, which record X-rays with energies between 700 and 7,000 electron volts in a combined exposure of three days, are shown in the two false-color strips above. Bluer colors indicate less intense X-ray emission. The dashed circle is 11.6 million light-years across and marks the so-called virial radius, where cold gas is now entering the cluster. Red circles indicate X-ray sources not associated with the cluster.
The results appear in today’s issue of Science.
The Perseus cluster (03hh 18m +41° 30‘) is the brightest extragalactic source of extended X-rays.
Lead author Aurora Simionescu, an astrophysicist at Stanford, and her colleagues note that until now, most observations of galaxy clusters have focused on their bright interiors. The Suzaku telescope was able to peer more closely at the outskirts of the Perseus cluster. The resulting census of baryonic matter (protons and neutrons of gas and metals) compared to dark matter offers some surprising observations.
It turns out the fraction of baryonic matter to dark matter at Perseus’s center was consistent with measurements for the universe as a whole, but the baryonic fraction unexpectedly exceeds the universal average on the cluster’s outskirts.
“The apparent baryon fraction exceeds the cosmic mean at larger radii, suggesting a clumpy distribution of the gas, which is important for understanding the ongoing growth of clusters from the surrounding cosmic web,” the authors write in the new paper.
Virtual Vesta. Taking their best guess, the science team on NASA’s Dawn Asteroid Orbiter have created a series of still images and videos (see below) to simulate what the protoplanet Vesta might look like. The exercise was carried out by mission planners at NASA's Jet Propulsion Laboratory and science team members at the German Aerospace Center and the Planetary Science Institute. Image credit: NASA/JPL-Caltech/ESA/UCLA/DLR/PSI/STScI/UMd
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The excitement is building as NASA’s innovative Dawn spacecraft closes in on its first protoplanetary target, the giant asteroid Vesta, with its camera eyes now wide open. The probe is on target to become the first spacecraft from Earth to orbit a body in the main asteroid belt and is set to arrive about four months from now in late July 2011.
Vesta is the second most massive object in the Asteroid Belt between Mars and Jupiter (map below). Since it is also one of the oldest bodies in our Solar System, scientists are eager to study it and search for clues about the formation and early history of the solar system. Dawn will spend about a year orbiting Vesta. Then it will fire its revolutionay ion thrusters and depart for Ceres, the largest asteroid in our solar system.
Dawn is equipped with three science instruments to photograph and investigate the surface mineralogy and elemental composition of the asteroid. The instruments were provided by the US, Germany and Italy. The spacecraft has just awoken from a six month hibernation phase. All three science instruments have been powered up and reactivated.
Dawn will image about 80 percent of Vesta’s surface at muliple angles with the onboard framing cameras to generate topographical maps. During the year in orbit, the probe will adjust its orbit and map the protoplanet at three different and decreasing altitudes between 650 and 200 kilometers, and thus increasing resolution. The cameras were provided and funded by Germany.
To prepare for the imaging campaign, mission planners from the US and Germany conducted a practice exercise to simulate the mission as though they were mapping Vesta. The effort was coordinated among the science and engineering teams at NASA’s Jet Propulsion Laboratory, the Institute of Planetary Research of the German Aerospace Center (DLR) in Berlin and the Planetary Science Institute in Tuscon, Ariz.
Simulated Vesta from the South Pole
This image shows the scientists' best guess to date of what the surface of the protoplanet Vesta might look like from the south pole, as projected onto a sphere 250 kilometers (160 miles) in radius. It was created as part of an exercise for NASA's Dawn mission involving mission planners at NASA's Jet Propulsion Laboratory and science team members at the Planetary Science Institute in Tuscon, Ariz. Credit: NASA/JPL-Caltech/UCLA/PSI
“We won’t know what Vesta really looks like until Dawn gets there,” said Carol Raymond in a NASA statement. Raymond is Dawn’s deputy principal investigator, based at JPL, who helped orchestrate the activity. “But we needed a way to make sure our imaging plans would give us the best results possible. The products have proven that Dawn’s mapping techniques will reveal a detailed view of this world that we’ve never seen up close before.”
Two teams worked independently and used different techniques to derive the topographical maps from the available data sets. The final results showed only minor differences in spatial resolution and height accuracy.
Using the best available observations from the Hubble Space Telescope and ground based telescopes and computer modeling techniques, they created maps of still images and a rotating animation (below) showing their best guess as to what Vesta’s surface actually looks like. The maps include dimples, bulges and craters based on the accumulated data to simulate topography and thus give a sense of Virtual Vesta in three dimensions (3 D).
“Working through this exercise, the mission planners and the scientists learned that we could improve the overall accuracy of the topographic reconstruction, using a somewhat different observation geometry,” said Nick Mastrodemo, Dawn’s optical navigation lead at JPL. “Since then, Dawn science planners have worked to tweak the plans to implement the lessons of the exercise.”
Dawn launch on September 27, 2007 by a Delta II rocket from Cape Canaveral Air Force Station, Florida. Credit: Ken KremerOf course no one will know how close these educated guesses come to matching reality until Dawn arrives at Vesta.
The framing camera system consists of two identical cameras developed and built by the Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany and the German Aerospace Center (DLR) in Berlin.
“The camera system is working flawlessly. The dry run was a complete success,” said Andreas Nathues, lead investigator for the framing camera at the Max Planck Institute in Katlenburg-Lindau, Germany.
Since the probe came out of hibernation, the mechanical and electrical components were checked out in mid March and found to be in excellent health and the software was updated.
Dawn is a mission of many firsts.
Dawn spacecraft under construction in Cleanroom.
Picture shows close up view of two science instruments;
The twin Framing Cameras at top (white rectangles) and VIR Spectrometer at right. Credit: Ken Kremer The spacecraft is NASA’s first mission specifically to the Asteroid Belt. It will become the first mission to orbit two solar system bodies.
The revolutionary Dawn mission is powered by exotic ion propulsion which is vastly more efficient than chemical propulsion thrusters. Indeed the ability to orbit two bodies in one mission is only enabled via the use of the ion engines fueled by xenon gas.
Vesta and Ceres are very different worlds that orbit between Mars and Jupiter. Vesta is rocky and may have undergone volcanism whereas Ceres is icy and may even harbor a subsurface ocean conducive to life.
Dawn will be able to comparatively investigate both celestial bodies with the same set of science instruments and try to unlock the mysteries of the beginnings of our solar system and why they are so different.
Dawn is part of NASA’sDiscovery program and was launched in September 2007 by a Delta II rocket from Cape Canaveral Air Force Station, Florida.
Virtual Vesta in 2 D.
This image shows a model of the protoplanet Vesta, using scientists' best guess to date of what the surface of the protoplanet might look like. The images incorporate the best data on dimples and bulges of Vesta from ground-based telescopes and NASA's Hubble Space Telescope. The cratering and small-scale surface variations are computer-generated, based on the patterns seen on the Earth's moon, an inner solar system object with a surface appearance that may be similar to Vesta. Credit: NASA/JPL-Caltech/UCLA/PSIVirtual Vesta in 3 D.
This anaglyph -- best viewed through red-blue glasses -- shows a 3-D model of the protoplanet Vesta, using scientists' best guess to date of what the surface of the protoplanet might look like. Image credit: NASA/JPL-Caltech/UCLA/PSI Dawn Spacecraft current location approaching Asteroid Vesta on March 21, 2011
Artist's impression of the binary brown dwarf system CFBDSIR 1458+10. Credit: ESO/L. Calçada
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Astronomers have found the coldest known star — a brown dwarf in a double system about as hot as a cup of tea. The discovery blurs the line between small cold stars and large hot planets. The star, CFBDSIR 1458+10B, is the dimmer member of the binary system, about 75 light-years from Earth.
Lead study author Michael Liu, from the University of Hawaii’s Institute for Astronomy, said finding ever-cooler stars “has been one of the big themes of this field since it’s existed in the last 15 years.” Brown dwarfs are essentially failed stars; they lack enough mass for gravity to trigger the nuclear reactions that make stars shine. Liu said while the idea of a brown dwarf is many decades old, they were first confirmed in 1995, the same year the first gas giants were detected around other stars.
“Residing at the extremes of low mass, luminosity and temperature, brown dwarfs serve as laboratories for understanding gas-giant extrasolar planets as well as the faint end of the star formation process,” write the authors in the new paper, in the Astrophysical Journal. “The coolest known brown dwarfs, the T dwarfs, have temperatures (~600–1400 K) … that are more akin to Jupiter than any star.”
Liu said cool brown dwarfs are exciting to find partly because they make great proxies for studying the mysteries of water cloud formation in the atmospheres of gas giants. Such clouds are believed to form when temperatures dip below 400 to 450 K.
“We probably will never get as detailed spectra from gas giants around other stars,” he said, “because the planets are gravitationally bound to their stars. It’s very hard to isolate the light from gas giant.” But brown dwarfs more often occur in isolation.
Three different telescopes were used to study the system: the ESO’s Very Large Telescope (VLT) in Chile, the Keck II Telescope in Hawaii and the Canada–France–Hawaii Telescope, also in Hawaii. The VLT was used to show that the composite object was very cool by brown dwarf standards.
“We were very excited to see that this object had such a low temperature, but we couldn’t have guessed that it would turn out to be a double system and have an even more interesting, even colder component,” said Philippe Delorme of the Institut de planétologie et d’astrophysique de Grenoble, a co-author of the paper.
CFBDSIR 1458+10 is the name of the binary system. The two components are known as CFBDSIR 1458+10A and CFBDSIR 1458+10B, with the latter the fainter and cooler of the two. They seem to be orbiting each other at a separation of about three times the distance between the Earth and the Sun in a period of about 30 years.
The dimmer of the two dwarfs has now been found to have a temperature of about 100 degrees Celsius, or about 370 K — the boiling point of water, and not much different from the temperature inside a sauna. By comparison the temperature of the surface of the Sun is about 5500 degrees Celsius.
The hunt for cool objects is a very active astronomical hot topic. The Spitzer Space Telescope has recently identified two other very faint objects as other possible contenders for the coolest known brown dwarfs, although their temperatures have not been measured so precisely. Future observations will better determine how these objects compare to CFBDSIR 1458+10B. Liu and his colleagues are planning to observe CFBDSIR 1458+10B again to better determine its properties and to begin mapping the binary’s orbit, which, after about a decade of monitoring, should allow astronomers to determine the binary’s mass.
Welcome to the scary and expensive world of buying your first, or replacing your old telescope!
I am asked all the time “What telescope should I buy” or “What telescope do I need to see X with?” Nine times out of ten, I recommend a Dobsonian Telescope.
So what is a Dobsonian telescope and why are they so good? Read on to find out why.
A Dobsonian is simplicity in itself; a simple set of optics on a simple mount. But don’t be fooled by this simplicity. Dobsonian telescopes are incredibly good and are great for amateurs and professional astronomers alike. They are also very economical compared to other telescopes.
The optical part of the telescope or OTA (Optical Tube Assembly) is the same as a Newtonian reflector telescope. It consists of a primary parabolic mirror and a flat secondary mirror in an open ended tube, with a focuser for an eyepiece set on the side. Light enters the tube, reflects off of the primary mirror at the base and is then focused onto the smaller flat secondary mirror and then finally, into an eyepiece. Simple!
Credit Skywatcher.net
The benefit of this type of optical arrangement is the telescopes light gathering ability. The more light gathered, equals more fainter objects to be seen. A light bucket!
Dobsonian/Newtonian telescopes have a big advantage over telescopes with lenses such as refractors and Cassegrain telescopes, as mirrors are a lot cheaper to make than lenses. Plus they can be a lot bigger!
Both Dobsonian and Newtonian telescopes are measured by the size of the diameter of their primary (big) mirror. Dobsonian sizes range from starter scopes of 6 inches up to 30 inches, but common sizes are 8 to 16 inches in diameter. They can be many times larger and less expensive to produce than scopes with lenses.
The second part of a Dobsonian telescope is the mount. As with the optical part the mount is just as simple, if not more so! A basic manual mount which supports the optical tube and can be manually moved by hand in the Altitude (up/down) and Azimuth (left/right) axis.
The mount is usually made from wood or metal with bearings and support for the two axis of movement. More so lately, some manufacturers have put GoTo systems with motors on some Dobsonian mounts. Personally I think it’s a bit over kill for a Dobsonian, as finding objects manually by star hopping or other manual methods helps you learn the sky better and can be fun.
Dobsonian
Resist the urge to spend lots of money on small computerized scopes that will eventually never get used, as they can be too complicated or you may not see much through them apart from the brightest objects such as the Moon. A Dobsonian is a great all-around telescope, and are available in almost all telescope stores. Some people make their own homemade Dobsonian scopes too!
Due to the nature of the Alt-Az mount, Dobsonians are not suitable for long exposure astro imaging. For that you will need an equatorial mount, which will track the stars equatorially. You may have some success with webcam imaging with some of the GoTo Mounts though.
Skywatcher 10 inch Dobsonian Credit sherwoods-photo.com
Dobsonian telescopes are designed to be simple, easy to use and gather as much light as possible. Because of this robust simplicity, they are very economical and popular with astronomers of all levels of ability. My own and most favourite telescope is my Skywatcher 10-inch Dobsonian and I will probably be using it for many more years to come, as it is difficult to beat!
The name of the Dobsonian telescope comes from its creator John Dobson, who combined the simple design of the Newtonian telescope with the Alt-Azimuth mount. He originally made simple homemade scopes from household materials and ground mirrors out of the glass of old ship portholes.
The original Hubble Ultra-Deep Field (Credit NASA, ESA, and S. Beckwith (STScI) and the HUDF Team).
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We live on a planet which orbits a star, and along with a hundred billion other stars, our Sun orbits the centre of our Milky Way galaxy. It doesn’t just stop there; our galaxy is one of hundreds of billions of galaxies in our Universe that gravitationally clump together in groups or clusters.
Throughout Spring in the northern hemisphere, astronomers and people interested in the night sky are going to be in for a galactic treat, as this is the time of year we can see the Coma/Virgo Super cluster or “Realm of Galaxies”.
Galaxies are massive islands of stars, gas and dust in the Universe; they are where stars and planets are born and eventually die. Galaxies are cosmic factories of creation — where it all happens on a very grand scale. To give you an idea of size, it would take you roughly 100,000 years to travel across the disc of the Milky Way at the speed of light!
Andromeda Galaxy.
The Milky Way is the second largest member of our local group of galaxies with Andromeda being the largest. Other members of our local group include the Triangulum galaxy and large and small Magellanic Clouds.
Virgo Galaxy Cluster - NOAO/AURA/NSF
The Coma/ Virgo Super cluster dominates our intergalactic neighbourhood; it represents the physical centre of our Local Super cluster and influences all the galaxies and galaxy groups by the gravitational attraction of its enormous mass.
Unfortunately galaxies are almost impossible to see with the naked eye, so you will need powerful binoculars or a large telescope, such as a Dobsonian to see most of the brighter galaxies in this region.
The cluster contains approximately 2,000 elliptical and spiral galaxies of which approximately 20 or more are observable using amateur equipment. This includes 16 Messier objects such as the Black eye spiral Galaxy M64, and elliptical galaxies, M86 with its plume, massive M87 at its centre and beautiful spiral M88, to name just a few.
From Left to Right M64, M86 and M88 (Credit NASA)
To find the approximate location of the Realm of Galaxies, first find the constellation of Leo – the lion — easily found in the South East this time of year with the backwards question mark overhis head. Go past Leo’s rear end and you will be in the bowl asterism of Virgo, to the bottom left of Leo and the faint constellation of Coma Berenices (Berenices hair) top left of Leo. This is the Realm of Galaxies!
Star Chart to help you find the Realm of Galaxies (Credit Adrian West)
Download a map of this region or use a star atlas to find your way around this area and try and spot as many galactic delights (faint fuzzies) as you can. As a bonus, the ringed Planet Saturn is just below this area too at the moment!
Give yourself plenty of time, wrap up warm and just think, you are looking for the largest structures in the Universe, hundreds of millions of light years away from Earth.
Newborn stars spew material into the surrounding gas and dust, creating a surreal landscape of glowing arcs, blobs and streaks — and ESO’s Very Large Telescope (VLT) has caught some of them on candid camera. This new image, released today, hails from NGC 6729, a nearby star-forming region in the constellation Corona Australis.
Star formation in the constellation of Corona Australis. Courtesy of ESO
The stellar nursery NGC 6729 (RA 19h 01m 54.1s; dec -36° 57′ 12″) is part of one of the closest stellar nurseries to Earth and therefore one of the best studied. The new VLT image gives a close-up view of a section of this strange and fascinating region.
The data were selected from the ESO archive by Sergey Stepanenko of the Ukraine, as part of the Hidden Treasures competition. The 2010 competition gave amateur astronomers the chance to search through ESO’s astronomical archives, hoping to find a well-hidden gem that needed polishing by the entrants. Participants vied for prizes, including a free trip to see the VLT in Chile for the overall winner. Stepanenko’s picture of NGC 6729 was ranked third.
Stars form deep within molecular clouds and the earliest stages of their development cannot be seen in visible-light telescopes because they kick out so much dust. Although very young stars at the upper left of the image cannot be seen directly, the havoc they have wreaked on their surroundings dominates the picture. High-speed jets of material that travel away from the baby stars at velocities as high as one million kilometers per hour are slamming into the surrounding gas and creating shock waves. The shocks cause the gas to shine and create the strangely-colored glowing arcs and blobs known as Herbig–Haro objects.
The astronomers George Herbig and Guillermo Haro were not the first to see one of the objects that now bear their names, but they were the first to study the spectra of these strange objects in detail. They realized that they were not just clumps of gas and dust that reflected light, or glowed under the influence of the ultraviolet light from young stars — but were a new class of objects associated with ejected material in star-forming regions.
Credit: ESO
In this view, the Herbig–Haro objects form two lines marking out the probable directions of ejected material. One stretches from the upper left to the lower center, ending in the bright, circular group of glowing blobs and arcs at the lower center. The other starts near the left upper edge of the picture and extends towards the center right. The peculiar sabre-shaped bright feature at the upper left is probably mostly due to starlight being reflected from dust and is not a Herbig–Haro object.
The enhanced-color picture was created from images taken using the VLT’s FORS1 instrument. Images were taken through two different filters that isolate the light coming from glowing hydrogen (shown as orange) and glowing ionized sulphur (shown as blue). The different colors in different parts of this violent star formation region reflect different conditions — for example where ionized sulphur is glowing brightly (blue features) the velocities of the colliding material are relatively low — and help astronomers to unravel what is going on in this dramatic scene.
Source: ESO press release. The paper, from the Astrophysical Journal, is available here.
At first glance, GJ 1214b is just another of the growing number of the super-Earth class of exoplanets. Discovered by the MEarth Project in 2009, it orbits an M dwarf in Ophiuchus in a tight orbit, swinging the planet around every 1.6 days. Late last year, GJ 1214b became the first super-Earth to have a component of its atmosphere detected when astronomers compared its spectra to models finding broad agreement with water vapor present. New work, done by the same team, further refines the atmosphere’s potential characteristics.
Previously, the team suggested that their observations could potentially fit with two hypothetical planet models. In the first, the planet could be covered in hydrogen and helium, but the lack of absorption features in the atmosphere’s spectra suggested that this were not the case unless this layer were hidden by thick clouds. However, from the data available, they could not conclusively rule out this possibility.
Combining their old observations with more recent ones from the MEarth Observatory, the team now reports that they have been able to rule out this scenario with a 4.5 σ confidence (over 99.99%). The result of this is that the remaining model, which contains higher amounts of “metals” (astronomy speak meaning all elements with atomic numbers higher than helium). The team also continues to support their earlier conclusion that the atmosphere is most likely at least 10% water vapor by volume, stating this with a 3 σ (or 99.7%) confidence based on the new observations. While water vapor may sound give the impression of being an inviting place for a tropical jungle, the team predicts the close orbiting planet would be a sweltering 535 degrees Fahrenheit.
While these findings are interesting stories of the atmosphere, the prevalence of such heavy elements may also give information relating to the structure and history of the planet itself. Models of planetary atmosphere suggest that, for planets of the mass and temperature expected for GJ 1214b, there are two primary formation scenarios. In the first, the atmosphere is directly accreted during the planet’s formation. However, this would indicate a hydrogen rich atmosphere and has been ruled out. The second is that the planet formed further out, beyond the “snow line”, as an icy body, but moved in after formation, creating the atmosphere from sublimated ices.
Although outside of the scope of their atmospheric research, the team also used the timing of the transits to search for wobbles in the orbit that could be caused by additional planets in the system. Ultimately, none were discovered.
Hubble has edged in close to the Tarantula Nebula, peering into its bright center of ionized gases, dust and still-forming stars. The Tarantula is already a go-to celestial marvel, because its hydrogen-fueled young stars shine with such intense ultraviolet light that they ionize and redden the surrounding gas — making the nebula visible without a telescope for Earth-bound observers 170,000 light-years away. The new image may make this popular beacon, in our neighboring galaxy the Large Magellanic Cloud, even more famous.
Credit: NASA, ESA
The wispy arms of the Tarantula Nebula (RA 05h 38m 38s dec -69° 05.7?) were originally thought to resemble spindly spider legs, giving the nebula its unusual name. The part of the nebula visible in the new image is criss-crossed with tendrils of dust and gas churned up by recent supernovae. These remnants include NGC 2060, visible above and to the left of the center of the image, which contains the brightest known pulsar.
The tarantula’s bite goes beyond NGC 2060. Near the edge of the nebula, outside the frame, below and to the right, lie the remains of supernova SN 1987a, the closest supernova to Earth to be observed since the invention of telescopes in the 17th century. Hubble and other telescopes have been returning to spy on this stellar explosion regularly since it blew up in 1987, and each subsequent visit shows an expanding shockwave lighting up the gas around the star, creating a pearl necklace of glowing pockets of gas around the remains of the star. SN 1987a is visible in wide field images of the nebula, such as that taken by the MPG/ESO 2.2-meter telescope.
A compact and extremely bright star cluster called RMC 136 lies above and to the left of this field of view, providing much of the radiation that powers the multi-coloured glow. Until recently, astronomers debated whether the source of the intense light was a tightly bound cluster of stars, or perhaps an unknown type of super-star thousands of times bigger than the sun. It is only in the last 20 years, with the fine detail revealed by Hubble and the latest generation of ground-based telescopes, that astronomers have been able to conclusively prove that it is, indeed, a star cluster.
But even if the Tarantula Nebula doesn’t contain this hypothetical super-star, it still hosts some extreme phenomena, making it a popular target for telescopes. Within the bright star cluster lies star RMC 136a1, which was recently found to be the heaviest ever discovered: the star’s mass when it was born was around 300 times that of the sun. This heavyweight is challenging astronomers’ theories of star formation, smashing through the upper limit they thought existed on star mass.
Astronomer James Elliot, a professor at MIT, has passed away at the age of 67. Elliot was part of a team of astronomers from Cornell University that discovered the rings around the planet Uranus in 1977. Elliot specialized in the techniques of planetary astronomy, particularly stellar occultations, to probe planetary atmospheres and the physical properties of small bodies in the outer solar system and beyond. Of particular interest to him was Pluto, Triton, Kuiper Belt objects and extrasolar planets. Steve Tilford from Steve’s Astro Corner knew Elliot personally and has written a very nice retrospective on Elliot’s life.
Hubble infrared image showing CL J1449+0856, the most distant mature cluster of galaxies found. Color data was added from ESO’s Very Large Telescope and the NAOJ’s Subaru Telescope. Credit: NASA, ESA, R. Gobat (Laboratoire AIM-Paris-Saclay, CEA/DSM-CNRS–)
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The galaxies above are among the oldest objects astronomers have ever laid eyes — er, telescopes — on, formed when the Universe was less than a quarter of its current age. In a new study out in the journal Astronomy & Astrophysics, a team of researchers has announced that they’ve used a fleet of the world’s most powerful telescopes to measure the distance from here to there.
And things look awfully familiar.
“The surprising thing is that when we look closely at this galaxy cluster it doesn’t look young — many of the galaxies have settled down and don’t resemble the usual star-forming galaxies seen in the early Universe,” said lead author Raphael Gobat of Université Paris Diderot in France.
The Very Large Telescope (VLT) at ESO's Cerro Paranal observing site in the Atacama Desert of Chile, consisting of four Unit Telescopes with main mirrors 8.2-m in diameter and four movable 1.8-m diameter Auxiliary Telescopes. The telescopes can work together, in groups of two or three, to form a giant interferometer, allowing astronomers to see details up to 25 times finer than with the individual telescopes. Credit: Iztok Boncina/ESO
Clusters of galaxies are the largest structures in the Universe that are held together by gravity. Astronomers expect these clusters to grow over time so that massive clusters would be rare in the early Universe. Although even more distant clusters have been seen, they appear to be young clusters in the process of formation, not settled mature systems.
The international team of astronomers used the powerful VIMOS and FORS2 instruments on ESO’s Very Large Telescope (VLT) to measure the distances to some of the blobs in a curious patch of very faint red objects first observed with the Spitzer space telescope. This grouping, named CL J1449+0856 for its position in the sky, had all the hallmarks of being a very remote cluster of galaxies. The results showed that we are indeed seeing a galaxy cluster as it was when the Universe was about three billion years old.
Once the team knew the distance to this very rare object, they looked carefully at the component galaxies using both Hubble and ground-based telescopes, including the VLT. They found evidence suggesting that most of the galaxies in the cluster were not forming stars, but were composed of stars that were already about one billion years old. This makes the cluster a mature object, similar in mass to the Virgo Cluster, the nearest rich galaxy cluster to the Milky Way.
Further evidence that this is a mature cluster comes from observations of X-rays coming from CL J1449+0856 made with ESA’s XMM-Newton space observatory. The cluster is giving off X-rays that must be coming from a very hot cloud of tenuous gas filling the space between the galaxies and concentrated towards the center of the cluster. This is another sign of a mature galaxy cluster, held firmly together by its own gravity, as very young clusters have not had time to trap hot gas in this way.
As Gobat concludes, “These new results support the idea that mature clusters existed when the Universe was less than one quarter of its current age. Such clusters are expected to be very rare according to current theory, and we have been very lucky to spot one. But if further observations find many more then this may mean that our understanding of the early Universe needs to be revised.”
