Abell 2744, shown above in a composite of images from the Hubble Space Telescope, the ESO’s Very Large Telescope and NASA’s Chandra X-ray Observatory, is one of the most complex and dramatic collisions ever seen between galaxy clusters.
X-ray image of Abell 2744
Dubbed “Pandora’s Cluster”, this is a region 5.9 million light-years across located 3.5 billion light-years away. Many different kinds of structures are found here, shown in the image as different colors. Data from Chandra are colored red, showing gas with temperatures in the millions of degrees. Dark matter is shown in blue based on data from Hubble, the European Southern Observatory’s VLT array and Japan’s Subaru telescope. Finally the optical images showing the individual galaxies have been added.
Even though there are many bright galaxies visible in the image, most of the mass in Pandora’s Cluster comes from the vast areas of dark matter and extremely hot gas. Researchers made the normally invisible dark matter “visible” by identifying its gravitational effects on light from distant galaxies. By carefully measuring the distortions in the light a map of the dark matter’s mass could be created.
Galaxy clusters are the largest known gravitationally-bound structures in the Universe, and Abell 2744 is where at least four clusters have collided together. The vast collision seems to have separated the gas from the dark matter and the galaxies themselves, creating strange effects which have never been seen together before. By studying the history of events like this astronomers hope to learn more about how dark matter behaves and how the different structures that make up the Universe interact with each other.
Check out this HD video tour of Pandora’s Cluster from the team at Chandra:
Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor or on Facebook for the most up-to-date astronomy awesomeness!
Space Shuttle Endeavour landed safely at the Kennedy Space Center on June 1, 2011 at 2:35 a.m. EDT. During the 16 day STS-134 mission, Endeavour delivered the $2 Billion Alpha Magnetic Spectrometer to the International Space Station and journeyed more than sixteen million miles. Endeavour was towed back to the Orbiter Processing Facility in preparation for display at her new retirement home at the California Science Center. Credit: Ken Kremer
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KENNEDY SPACE CENTER – Space Shuttle Endeavour and her six man crew landed safely today at the Kennedy Space Center in Florida at 2:35 a.m. EDT following a 16 day journey of more than sixteen million miles.
The STS-134 mission marked the end of Endeavour’s space exploration career. It was the 25th and last space mission by NASA’s youngest orbiter. Altogether, Endeavour has logged 299 days in space, orbited Earth 4,671 times and traveled 122,883,151 miles.
The crew was led by Shuttle Commander Mark Kelly. Also aboard were Pilot Greg H. Johnson and Mission Specialists Mike Fincke, Drew Feustel, Greg Chamitoff and the European Space Agency’s Roberto Vittori. Vittori is the last non NASA astronaut to fly on a shuttle mission.
The night landing capped a highly productive flight highlighted by the delivery of the $2 Billion Alpha Magnetic Spectrometer (AMS) to the International Space Station. AMS is a cosmic ray detector that seeks to unveil the invisible universe and search for evidence of dark matter, strange matter and antimatter.
5 of 6 crew members of STS-134 mission of Space Shuttle Endeavour at post landing press briefing. Credit: Ken Kremer
“What a great ending to this really wonderful mission,” said Bill Gerstenmaier, associate administrator for Space Operation at a briefing today for reporters “They’re getting great data from their instrument on board the space station. It couldn’t have gone any better for this mission.”
Mike Leinbach, the Space Shuttle Launch Director, said, “It’s been a great morning at the Kennedy Space Center. Commander Kelly and his crew are in great spirits.”
During the flight, Mike Fincke established a new record of 382 days for time a U.S. astronaut has spent in space. He broke the record on May 27, his 377th day on May 27, by surpassing previous record holder Peggy Whitson.
STS-134 was the 134th space shuttle mission and the 36th shuttle mission dedicated to ISS assembly and maintenance.
“You know, the space shuttle is an amazing vehicle, to fly through the atmosphere, hit it at Mach 25, steer through the atmosphere like an airplane, land on a runway, it is really, really an incredible ship,” said Kelly.
“On behalf of my entire crew, I want to thank every person who’s worked to get this mission going and every person who’s worked on Endeavour. It’s sad to see her land for the last time, but she really has a great legacy.”
After the landing at the Shuttle Landing Facility (SLF) , Endeavour was towed back into the Orbiter Processing Facility (OPF) where she will be cleaned and “safed” in preparation for her final resting place – Retirement and public display at the California Science Center in Los Angelos, California.
With the successful conclusion of Endeavour’s mission, the stage is now set for blastoff of the STS-135 mission on July 8, the very final flight of the three decade long shuttle Era.
“We’ve had a lot going on here,” said Mike Moses, space shuttle launch integration manager, “Being able to send Atlantis out to the pad and then go out and land Endeavour was really a combination I never expected to have.
It’s been a heck of a month in the last 4 hours !”
Shuttle Endeavour Landing Photos by Mike Deep for Universe Today
STS-134 Space Shuttle Commander Mark Kelly. Credit: Ken Kremer STS-134 Endeavour Post Landing Press Briefing.
Bill Gerstenmaier, NASA Associate Administrator for Space Operations, Mike Moses, Space Shuttle launch integration manager at NASA KSC, Mike Leinbach, Space Shuttle Launch Director at NASA KSC, laud the hard work and dedication of everyone working on the Space Shuttle program. Credit: Ken Kremer
Read my related stories about the STS-134 mission here:
Comic Microwave Background Courtesy of NASA / WMAP Science Team
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Not since the work of Fritz Zwicky has the astronomy world been so excited about the missing mass of the Universe. His evidence came from the orbital velocities of galaxies in clusters, rotational speeds, and gravitational lensing of background objects. Now there’s even more evidence that Zwicky was right as Australian student – Amelia Fraser-McKelvie – made another breakthrough in the world of astrophysics.
Working with a team at the Monash School of Physics, the 22-year-old undergraduate Aerospace Engineering/Science student conducted a targeted X-ray search for the hidden matter and within just three months made a very exciting discovery. Astrophysicists predicted the mass would be low in density, but high in temperature – approximately one million degrees Celsius. According to theory, the matter should have been observable at X-ray wavelengths and Amelia Fraser-McKelvie’s discovery has proved the prediction to be correct.
Dr Kevin Pimbblet from the School of Astrophysics explains: “It was thought from a theoretical viewpoint that there should be about double the amount of matter in the local Universe compared to what was observed. It was predicted that the majority of this missing mass should be located in large-scale cosmic structures called filaments – a bit like thick shoelaces.”
Up until this point in time, theories were based solely on numerical models, so Fraser-McKelvie’s observations represent a true break-through in determining just how much of this mass is caught in filamentary structure. “Most of the baryons in the Universe are thought to be contained within filaments of galaxies, but as yet, no single study has published the observed properties of a large sample of known filaments to determine typical physical characteristics such as temperature and electron density.” says Amelia. “We examine if a filament’s membership to a supercluster leads to an enhanced electron density as reported by Kull & Bohringer (1999). We suggest it remains unclear if supercluster membership causes such an enhancement.”
Still a year away from undertaking her Honors year (which she will complete under the supervision of Dr Pimbblet), Ms Fraser-McKelvie is being hailed as one of Australia’s most exciting young students… and we can see why!
The AMS sits near the center of this graphic, which shows where the experiment is located on the truss of the ISS. Credit: NASA
The long-awaited Alpha Magnetic Spectrometer, a particle physics detector that could unlock mysteries about dark matter and other cosmic radiation, has now been installed outside the International Space Station. It is the largest and most complex scientific instrument yet on board the orbiting laboratory, and will examine ten thousand cosmic-ray hits every minute, looking for nature’s best-kept particle secrets, searching for clues into the fundamental nature of matter.
“Thank you very much for the great ride and safe delivery of AMS to the station,” said Dr. Samuel Ting, speaking via radio to the crew on orbit who installed the AMS. Ting is the AMS Principal Investigator who has worked on the project for close to 20 years. “Your support and fantastic work have taken us one step closer to realizing the science potential of AMS. With your help, for the next 20 years, AMS on the station will provide us a better understanding of the origin of the universe.”
“Thank you, Sam,” Endeavour commander Mark Kelly radioed back, “I was just looking out the window of the orbiter and AMS looks absolutely fantastic on the truss. I know you guys are really excited and you’re probably getting data and looking at it already.”
By collecting and measuring vast numbers of cosmic rays and their energies, particle physicists hope to understand more about how and where they are born, since a long-standing mystery is where cosmic rays originate. They could be created in the magnetic fields of exploded stars, or perhaps in the hearts of active galaxies, or maybe in places as yet unseen by astronomers.
The AMS is actually AMS-02 – a prototype of the instrument, AMS-01, was launched on board the space shuttle in 1998, and showed great potential. But Ting and his collaborators from around the world knew that to make a significant contribution to particle science, they needed a detector that could be in space for a long period of time.
AMS-02 will operate on the ISS until at least 2020, and hopefully longer, depending on the life of the space station.
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The AMS will also search for antimatter within the cosmic rays, and attempt to determine whether the antimatter is formed from collisions between particles of dark matter, the mysterious substance that astronomers believe may make up about 22% of the Universe.
There is also the remote chance that AMS-02 will detect a particle of anti-helium, left over from the Big Bang itself.
“The most exciting objective of AMS is to probe the unknown; to search for phenomena which exist in nature that we have not yet imagined nor had the tools to discover,” said Ting.
Could assessing the orbital motion of red dwarf binaries offer support for fringe science? Probably not. Credit: NASA.
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The Sloan Low-mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES) catalog was recently announced, containing 1,342 common proper motion pairs (i.e. binaries) – which are all low mass stars in the mid-K and mid-M stellar classes – in other words, orange and red dwarves.
These low mass pairs are all at least 500 astronomical units distance from each other – at which point the mutual gravitation between the two objects gets pretty tenuous – or so Newton would have it. Such a context provides a test-bed for something that lies in the realms of ‘fringe science’ – that is, Modified Newtonian Dynamics, or MoND.
The origin of MoND theory is generally attributed to a paper by Milgrom in 1981, which proposed MoND as an alternative way to account for the dynamics of disk galaxies and galactic clusters. Such structures can’t obviously hold together, with the rotational velocities they possess, without the addition of ‘invisible mass’ – or what these days we call dark matter.
MoND seeks to challenge a fundamental assumption built into both Newton’s and Einstein’s theories of gravity – where the gravitational force (or the space-time curvature) exerted by a massive object recedes by the inverse square of the distance from it. Both theories assume this relationship is universal – it doesn’t matter what the mass is or what the distance is, this relationship should always hold.
In a roundabout way, MoND proposes a modification to Newton’s Second Law of Motion – where Force equals mass times acceleration (F=ma) – although in this context, a is actually representing gravitational force (which is expressed as an acceleration).
If a expresses gravitational force, then F expresses the principle of weight. So for example, you can easily exert a sufficient force to lift a brick off the surface of the Earth, but it’s unlikely that you will be able to lift a brick, with the same mass, off the surface of a neutron star.
Anyhow, the idea of MoND is that by allowing F=ma to have a non-linear relationship at low values of a, a very tenuous gravitational force acting across a great distance might still be able to hold something in a loose orbit around a galaxy, despite the principle of a linear F=ma relationship predicting that this shouldn’t happen.
Left image: The unusual flat curve (B) of velocities of objects in disk galaxies versus what would be expected by a naive application of Kepler's Third Law (A). Right image: A scatter plot of selected binaries from the SLoWPoKE catalogue (blue) plotted against the trend expected by Kepler's Third Law (red). Credit: Hernandez et al. (Author's note - Kepler's Third Law of Planetary Motion fits the context of the solar system where 99% of the mass is contained in the Sun. Its applicability to the motion of stars in a galactic disk, with a much more even mass distribution, is uncertain)
MoND is fringe science, an extraordinary claim requiring extraordinary evidence, since if Newton’s or Einstein’s theories of gravity cannot be assumed to universal, a whole bunch of other physical, astrophysical and cosmological principles start to unravel.
Also, MoND doesn’t really account for other observational evidence of dark matter – notably the gravitational lensing seen in different galaxies and galactic clusters – a degree of lensing that exceeds what is expected from the amount of visible mass that they contain.
In any case, Hernandez et al have presented a data analysis drawn from the SLoWPoKES database of widely spread low-mass binaries, suggestive that MoND might actually work at scales of around 7000 astronomical units. Now, since this hasn’t yet been picked up by Nature, Sci. Am. or anyone else of note – and since some hack writer at Universe Today is just giving it a ‘balanced’ review here, it may be premature to consider that a major paradigm of physics has been overturned.
Nonetheless, the concept of ‘missing mass’ and dark matter has been kicked around for close on 90 years now – with no-one seemingly any closer to determining what the heck this stuff is. On this basis, it is reasonable to at least entertain some alternate views.
President Obama plans to attend the last launch of Endeavour on April 29, 2011 at the Kennedy Space Center. President Obama last visited the Kennedy Space Center in Florida on April 15, 2010 and outlined the new course his administration is charting for NASA and the future of U.S. human spaceflight. Credit: NASA/Kim Shiflett
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President Barack Obama and the entire First Family apparently plan to attend the final launch of Space Shuttle Endeavour, according to government officials and multiple news outlets. Endeavour is slated to blast off on the STS-134 mission next Friday, April 29 from the Kennedy Space Center (KSC) in Florida at 3:47 p.m. EDT.
There has already been intense drama surrounding the STS-134 mission because it is being commanded by Mark Kelly. Kelly is the husband of U.S. Congresswoman Gabrielle Giffords of Arizona who was critically wounded by gunshots to her head at point blank range during an assassination attempt while attending a meet and greet with her constituents on Jan. 8, 2011. Six people – including a nine year old girl and a federal judge – were killed and a dozen more were wounded that awful day.
Space Shuttle Endeavour awaits her final launch on April 29, 2011 from Pad 39A at the Kennedy Space Center, FL Credit: Ken Kremer
The Presidents appearance at the STS-134 launch will almost certainly lead to skyrocketing interest, but has not yet been officially announced by NASA and the White House. The event is not yet listed on the presidents official schedule.
However, a tweet by the staff of Congresswoman Giffords on her official website states Obama will attend; “We are very happy that Pres. Obama is coming to Mark’s launch! This historic mission will be #Endeavours final flight.”
NASA spokesman Allard Beutel told me today, “I cannot confirm whether the president will be coming to launch next week. If he’s coming, which I can’t confirm, we are a White House agency.”
“We always welcome a visit from the President,” Beutel said.
Security is always tight at KSC during a shuttle launch. A visit by President Obama will certainly lead to even tighter security controls and even more massive traffic jams.
Giant crowds were already expected for this historic final spaceflight of Space Shuttle Endeavour, NASA’s youngest Orbiter, on her 25th mission to space.
Endeavour is carrying the $2 Billion Alpha Magnetic Spectrometer (AMS) ) on a 14-day flight to the International Space Station, a premier science instrument that will collect cosmic rays, search for dark energy, dark matter and anti matter and seeks to determine the origin of the Universe. See my photo below of the AMS from inside the Space Station Processing Facility (SSPF) at KSC with the principal investigator, Nobel Prize winner Prof. Sam Ting of MIT.
President Obama last visited KSC on April 15, 2010 and gave a major policy speech outlining his radical new human spaceflight goals for NASA. Obama decided to cancel NASA’s Project Constellation ‘Return to the Moon’ Program and the Ares 1 and Ares 5 rockets. He directed NASA to plan a mission for astronauts to visit an Asteroid by 2025 and one of the moons of Mars in the 2030’s. Obama also decided to revive the Orion crew module built by Lockheed Martin, which is now envisaged for missions beyond low earth orbit (LEO), and invest in development of new commercial space taxis such as the Dragon spacecraft by SpaceX for transporting astronaut crews to the ISS.
Spokesman Beutel said that during the April 2010 visit, “The President met with space workers.” He could not comment on details of the president’s plans for the STS-134 visit and said information would have to come from the White House.
The last time a sitting president watched a live human space launch was in 1998 when then President Bill Clinton attended the blastoff of the return to space of Astronaut and Senator John Glenn. Glenn was the first American to orbit the Earth back in 1962. Glenn’s first flight took place a little over a year after the historic first human spaceflight by Soviet Cosmonaut Yuri Gagarin on April 12, 1961- which occurred exactly 50 years ago last week.
Congresswoman Giffords is recovering from her wounds and Shuttle Commander Kelly has said that she would like to attend the STS-134 launch. But no official announcement about her attendance has been made by NASA and depends on many factors including decisions by the doctors treating her in a Houston area hospital.
The Alpha Magnetic Spectrometer (AMS) and Nobel Prize Winner and Principal Investigator Sam Ting of MIT - inside the Space Station Processing Facility at KSC. The STS-134 mission of shuttle Endeavour will deliver the AMS to the ISS. The AMS purpose is to try and determine the origin of the Universe. . Credit: Ken KremerClose up of Endeavour crew cabin, ET, SRB and astronaut walkway to the White Room. Credit: Ken Kremer
Illustration of Antimatter/Matter Annihilation. (NASA/CXC/M. Weiss)
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Since the late 20th century, astronomers have been aware of data that suggest the universe is not only expanding, but expanding at an accelerating rate. According to the currently accepted model, this accelerated expansion is due to dark energy, a mysterious repulsive force that makes up about 73% of the energy density of the universe. Now, a new study reveals an alternative theory: that the expansion of the universe is actually due to the relationship between matter and antimatter. According to this study, matter and antimatter gravitationally repel each other and create a kind of “antigravity” that could do away with the need for dark energy in the universe.
Massimo Villata, a scientist from the Observatory of Turin in Italy, began the study with two major assumptions. First, he posited that both matter and antimatter have positive mass and energy density. Traditionally, the gravitational influence of a particle is determined solely by its mass. A positive mass value indicates that the particle will attract other particles gravitationally. Under Villata’s assumption, this applies to antiparticles as well. So under the influence of gravity, particles attract other particles and antiparticles attract other antiparticles. But what kind of force occurs between particles and antiparticles?
To resolve this question, Villata needed to institute the second assumption – that general relativity is CPT invariant. This means that the laws governing an ordinary matter particle in an ordinary field in spacetime can be applied equally well to scenarios in which charge (electric charge and internal quantum numbers), parity (spatial coordinates) and time are reversed, as they are for antimatter. When you reverse the equations of general relativity in charge, parity and time for either the particle or the field the particle is traveling in, the result is a change of sign in the gravity term, making it negative instead of positive and implying so-called antigravity between the two.
Villata cited the quaint example of an apple falling on Isaac Newton’s head. If an anti-apple falls on an anti-Earth, the two will attract and the anti-apple will hit anti-Newton on the head; however, an anti-apple cannot “fall” on regular old Earth, which is made of regular old matter. Instead, the anti-apple will fly away from Earth because of gravity’s change in sign. In other words, if general relativity is, in fact, CPT invariant, antigravity would cause particles and antiparticles to mutually repel. On a much larger scale, Villata claims that the universe is expanding because of this powerful repulsion between matter and antimatter.
What about the fact that matter and antimatter are known to annihilate each other? Villata resolved this paradox by placing antimatter far away from matter, in the enormous voids between galaxy clusters. These voids are believed to have stemmed from tiny negative fluctuations in the primordial density field and do seem to possess a kind of antigravity, repelling all matter away from them. Of course, the reason astronomers don’t actually observe any antimatter in the voids is still up in the air. In Villata’s words, “There is more than one possible answer, which will be investigated elsewhere.” The research appears in this month’s edition of Europhysics Letters.
Bottom photomultiplier tube array on the XENON 100 detector. Credit: the XENON collaboration
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We’re still mostly in the dark about Dark Matter, and the highly anticipated results from the XENON100 detector has perhaps shed a tad more light on the subject – by not making a detection in the first 100 days of the experiment. Researchers from the project say they have now been able to place the most stringent limits yet on the properties of dark matter.
To look for any possible hints of Dark Matter interacting with ordinary matter, the project has been looking for WIMPS — or weakly interacting massive particles – but for now, there is no new evidence for the existence of WIMPS, or Dark Matter either.
The extremely sensitive XENON100 detector is buried beneath the Gran Sasso mountain in central Italy, shielding it from cosmic radiation so it hopefully can detect WIMPS, hypothetical particles that might be heavier than atomic nuclei, and the most popular candidate for what Dark Matter might be made of. The detector consists of 62 kg of liquid xenon contained within a heavily shielded tank. If a WIMP would enter the detector, it should interact with the xenon nuclei to generate light and electric signals – which would be a kind of “You Have Won!” indicator.
Dark Matter is thought to make up more than 80% of all mass in the universe, but the nature of it is still unknown. Scientists believe that it is made up of exotic particles unlike the normal (baryonic) matter, which we, the Earth, Sun and stars are made of, and it is invisible so it has only been inferred from its gravitational effects.
The XENON detector ran from January to June 2010 for its first run, and in their paper on arxiv, the team revealed they found three candidate events that might be due to Dark Matter. But two of these were expected to appear anyway because of background noise, the team said, so their results are effectively negative.
Does this rule out the existence of WIMPS? Not necessarily – the team will keep working on their search. Plus, results from a preliminary analysis from11.2 days worth of data, taken during the experiment’s commissioning phase in October and November 2009, already set new upper limits on the interaction rate of WIMPs – the world’s best for WIMP masses below about 80 times the mass of a proton.
And the XENON100 team was optimistic. “These new results reveal the highest sensitivity reported as yet by any dark matter experiment, while placing the strongest constraints on new physics models for particles of dark matter,” the team said in a statement.
A1689-zD1, one of the brightest and most distant galaxies, is 12.8 billion light years away - an extremely far distance in our expanding universe. Image credit: NASA/ESA/JPL-Caltech/STScI
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Welcome back to the third, and last, installment of Cosmology 101. So far, we’ve covered the history of the universe up to the present moment. But what happens next? How will our universe end? And how can we be so sure that this is how the story unfolded?
Robert Frost once wrote, “Some say the world will end in fire; some say in ice.” Likewise, some scientists have postulated that the universe could die either a dramatic, cataclysmic death – either a “Big Rip” or a “Big Crunch” – or a slower, more gradual “Big Freeze.” The ultimate fate of our cosmos has a lot to do with its shape. If the universe were open, like a saddle, and the energy density of dark energy increased without bound, the expansion rate of the cosmos would eventually become so great that even atoms would be torn apart – a Big Rip. Conversely, if the universe were closed, like a sphere, and gravity’s strength trumped the influence of dark energy, the outward expansion of the cosmos would eventually come to a halt and reverse, collapsing on itself in a Big Crunch.
Despite the poetic beauty of fire, however, current observations favor an icy end to our universe – a Big Freeze. Scientists believe that we live in a spatially flat universe whose expansion is accelerating due to the presence of dark energy; however, the total energy density of the cosmos is most likely less than or equal to the so-called “critical density,” so there will be no Big Rip. Instead, the contents of the universe will eventually drift prohibitively far away from each other and heat and energy exchange will cease. The cosmos will have reached a state of maximum entropy, and no life will be able to survive. Depressing and a bit anti-climactic? Perhaps. But it probably won’t be perceptible until the universe is at least twice its current age.
At this point you might be screaming, “How do we know all this? Isn’t it all just rampant speculation?” Well, first of all, we know without a doubt that the universe is expanding. Astronomical observations consistently demonstrate that light from distant stars is always redshifted relative to us; that is, its wavelength has been stretched due to the expansion of the cosmos. This leads to two possibilities when you wind back the clock: either the expanding universe has always existed and is infinite in age, or it began expanding from a smaller version of itself at a specific time in the past and thus has a fixed age. For a long time, proponents of the Steady State Theory endorsed the former explanation. It wasn’t until Arno Penzias and Robert Wilson discovered the cosmic microwave background in 1965 that the big bang theory became the most accepted explanation for the origin of the universe.
Why? Something as large as our cosmos takes quite a while to cool completely. If the universe did, in fact, began with the kind of blistering energies that the big bang theory predicts, astronomers should still see some leftover heat today. And they do: a uniform 3K glow evenly dispersed at every point in the sky. Not only that – but WMAP and other satellites have observed tiny inhomogeneities in the CMB that precisely match the initial spectrum of quantum fluctuations predicted by the big bang theory.
What else? Take a look at the relative abundances of light elements in the universe. Remember that during the first few minutes of the cosmos’ young life, the ambient temperature was high enough for nuclear fusion to occur. The laws of thermodynamics and the relative density of baryons (i.e. protons and neutrons) together determine exactly how much deuterium (heavy hydrogen), helium and lithium could be formed at this time. As it turns out, there is far more helium (25%!) in our current universe than could be created by nucleosynthesis in the center of stars. Meanwhile, a hot early universe – like the one postulated by the big bang theory – gives rise to the exact proportions of light elements that scientists observe in the universe today.
But wait, there’s more. The distribution of large-scale structure in the universe can be mapped extremely well based solely on observed anisotropies in the CMB. Moreover, today’s large-scale structure looks very different from that at high redshift, implying a dynamic and evolving universe. Additionally, the age of the oldest stars appears to be consistent with the age of the cosmos given by the big bang theory. Like any theory, it has its weaknesses – for instance, the horizon problem or the flatness problem or the problems of dark energy and dark matter; but overall, astronomical observations match the predictions of the big bang theory far more closely than any rival idea. Until that changes, it seems as though the big bang theory is here to stay.
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.
