Posted on by Steve Nerlich

Astronomy Without A Telescope – Backgrounds

Thousands of galaxies observed by the Herschel Space Observatory through the Lockman hole. Credit: ESA.

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You’ve probably heard of the cosmic microwave background, but it doesn’t stop there. The as-yet-undetectable cosmic neutrino background is out there waiting to give us a view into the first seconds after the Big Bang. Then, looking further forward, there are other backgrounds across the electromagnetic spectrum – all of which contribute to what’s called the extragalactic background light, or EBL.

The EBL is the integrated whole of all light that has ever been radiated by all galaxies across all of time. At least, all of time since stars and galaxies first came into being – which was after the dark ages that followed the release of the cosmic microwave background.

The cosmic microwave background was released around 380,000 years after the Big Bang. The dark ages may have then persisted for another 750 million years, until the first stars and the first galaxies formed.

In the current era, the cosmic microwave background is estimated to make up about sixty percent of the photon density of all background radiation in the visible universe – the remaining forty per cent representing the EBL, that is the radiation contributed by all the stars and galaxies that have appeared since.

This gives some indication of the enormous burst of light that the cosmic microwave background represented, although it has since been red-shifted into almost invisibility over the subsequent 13.7 billion years. The EBL is dominated by optical and infrared backgrounds, the former being starlight and the latter being dust heated by that starlight which emits infrared radiation.

Just like the cosmic microwave background can tell us something about the evolution of the earlier universe, the cosmic infrared background can tell us something about the subsequent evolution of the universe – particularly about the formation of the first galaxies.

The power density of the universe's background radiation plotted over wavelength. The cosmic microwave background, though substantially red-shifted due to its age, still dominates. The remainder, extragalactic background light, is dominated by optical and infrared radiation, which have power densities several orders of magnitude higher than the remaining radiation wavelengths.

The Photodetector Array Camera and Spectrometer (PACS) Evolutionary Probe is a ‘guaranteed time’ project for the Herschel Space Observatory. Guaranteed means there always a certain amount of telescope time dedicated to this project regardless of other priorities. The PACS Evolutionary Probe project, or just PEP, aims to survey the cosmic infrared background in the relatively dust free regions of the sky that include: the Lockman Hole; the Great Observatories Origins Deep Survey (GOODS) fields; and the Cosmic Evolution Survey (COSMOS) field.

The Herschel PEP project is collecting data to enable determination of rest frame radiation of galaxies out to a redshift of about z =3, where you are observing galaxies when the universe was about 3 billion years old. Rest frame radiation means making an estimation of the nature of the radiation emitted by those early galaxies before their radiation was red-shifted by the intervening expansion of the universe.

The data indicate that infrared contributes around half of the total extragalactic background light. But if you just look at the current era of the local universe, infrared only contributes one third. This suggests that more infrared radiation was produced in the distant past, than in the present era.

This may be because earlier galaxies had more dust – while modern galaxies have less. For example, elliptical galaxies have almost no dust and radiate almost no infrared. However, luminous infrared galaxies (LIRGs) radiate strongly in infrared and less so in optical, presumably because they have a high dust content.

Modern era LIRGs may result from galactic mergers which provide a new supply of unbound dust to a galaxy, stimulating new star formation. Nonetheless, these may be roughly analogous to what galaxies in the early universe looked like.

Dustless, elliptical galaxies are probably the evolutionary end-point of an galactic merger, but in the absence of any new material to feed off these galaxies just contain aging stars.

So it seems that having a growing number of elliptical galaxies in your backyard is a sign that you live in a universe that is losing its fresh, infrared flush of youth.

Further reading: Berta et al Building the cosmic infrared background brick by brick with Herschel/PEP

Posted on by Steve Nerlich

Astronomy Without A Telescope – Enough With The Dark Already

It's confirmed that the universe is expanding with a uniform acceleration. Dark energy... not so much. Credit: Swinburne University.

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The recent WiggleZ galaxy survey data further confirming that the universe is expanding with a uniform acceleration prompted a lot of ‘astronomers confirm dark energy’ headlines and a lot of heavy sighs from those preferring not to have the universe described in ten words or less.

I mean how the heck did ‘dark energy’ ever become shorthand for ‘the universe is expanding with a uniform acceleration’?

These ‘dark energy confirmed’ headlines risk developing a popular view that the universe is some kind of balloon that you have to pump energy into to make it expand. This is not an appropriate interpretation of the dark energy concept – which only came into common use after 1998 when Type 1a supernova data were announced, suggesting an accelerating expansion of the universe.

It was widely accepted well before then that the universe was expanding. A prevalent view before 1998 was that expansion might be driven by the outward momentum of the universe’s contents – a momentum possibly established from the initial cosmic inflation event that followed the Big Bang.

Current thinking on the expansion of the universe does not associate its expansion to the momentum of its contents. Instead the universe is thought of as raisin toast dough which expands in an oven – not because the raisins are pushing the dough outwards, but because the dough itself expands and as a consequence the distance between the raisins (i.e. galaxies etc) increases.

It’s not a perfect analogy since space-time is not a substance – and, at the level of a universe, the heat of the oven equates to the input of energy out of nowhere – and being thermal energy, it’s not dark.

Alternatively, you can model the universe as a perfect fluid where you think of dark energy as a negative pressure (since a positive pressure would compress the fluid). A negative pressure does not obviously require additional contents to be pumped into the fluid universe, although the physical nature of a ‘negative pressure’ in this context is yet to be explained.

Various possible shapes of the observable universe - where mass/energy density is too high, too low or just right (omega = 1), so that the geometry is Euclidean and the three angles of a triangle do add up to 180 degrees. Our universe does appear to have a flat Euclidean geometry, but it doesn't have enough visible mass/energy required to make it flat. Hence, we assume there must be a lot of dark stuff out there.

The requirement for dark energy in standard model cosmology is to sustain the observable flat geometry of space – which is presumed to be sustained by the mass-energy contents of the universe. Too much mass-energy should give a spherical shape to space, while too little mass-energy should give a hyperboloid shape.

So, since the universe is flat – and stays flat in the face of accelerating expansion, there must be a substantial ‘dark’ (i.e. undetectable) component. And it seems to be a component that grows as the universe increases in volume, in order to sustain that flat geometry – at least in current era of the universe’s evolution.

It is called ‘energy’ as it is evenly distributed (i.e. not prone to clumping, like dark matter), but otherwise it has no analogous properties with any form of energy that we know about.

More significantly, from this perspective, the primary requirement for dark energy is not as a driver of expansion, but as a hypothetical entity required to sustain the flatness of space in the face of expansion. This line of thinking then begs the question of just what does drive the accelerating expansion of the universe. And an appropriate answer to that question is – we haven’t a clue.

A plausible mechanism that accounts for the input of energy out of nowhere – and a plausible form of energy that is both invisible and that somehow generates the production of more space-time volume are all required to support the view that dark energy underlies the universe’s accelerating expansion.

Not saying it’s impossible, but no way has anyone confirmed that dark energy is real. Our flat universe is expanding with a uniform acceleration. For now, that is the news story.

Further reading:
Expansion of the universe
Shape of the universe

Posted on by VirtualAstro

Supernova Discovered in M51 The Whirlpool Galaxy

M51 Hubble Remix

A new supernova (exploding star) has been discovered in the famous Whirlpool Galaxy, M51.

M51, The Whirlpool galaxy is a galaxy found in the constellation of Canes Venatici, very near the star Alkaid in the handle of the saucepan asterism of the big dipper. Easily found with binoculars or a small telescope.

The discovery was made on June 2nd by French astronomers and the supernova is reported to be around magnitude 14. More information (In French) can be found here or translated version here.

Image by BBC Sky at Night Presenter Pete Lawrence

The supernova will be quite tricky to spot visually and you may need a good sized dobsonian or similar telescope to spot it, but it will be a easy target for those interested in astro imaging.

The whirlpool galaxy was the first galaxy discovered with a spiral structure and is one of the most recognisable and famous objects in the sky.

Posted on by Ken Kremer

Era of Space Shuttle Endeavour Ends with June 1 landing at the Kennedy Space Center

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.”

Four members of the crew conducted 4 spacewalks during the flight, which were the last by shuttle crew members during the space shuttle era. Simultaneously they completed the construction of the US portion of the ISS.

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:

Amazing Photos and Milestone Tributes Mark Last Space Shuttle Spacewalk
Awesome Hi Def Launch Videos from Endeavour
Spectacular Soyuz Photo Gallery shows Unprecedented View Of Shuttle Docked at Station
Ultimate ISS + Shuttle + Earth Photo Op Coming on May 23 from Soyuz and Paolo Nespoli
Endeavour Blasts Off on Her 25th and Final Mission
Endeavour Unveiled for Historic Final Blastoff
Looking to the Heavens with Endeavour; Launch Pad Photo Special
Endeavour Astronauts Arrive at Cape for May 16 Launch
NASA Sets May 16 for Last Launch of Endeavour; Atlantis Slips to July
Endeavour’s Final Launch further delayed another Week or more
On the Cusp of Endeavour’s Final Flight
Brush Fires Erupt at Kennedy Space Center during Endeavour’s Last Countdown
Commander Mark Kelly and STS-134 Crew Arrive at Kennedy for Endeavour’s Final Flight
President Obama to Attend Endeavour’s Last Launch on April 29
Shuttle Endeavour Photo Special: On Top of Pad 39A for Final Flight
Endeavour Mated to Rockets for Last Flight Photo Album
Endeavour Rolls to Vehicle Assembly Building for Final Flight

Posted on by Steve Nerlich

Astronomy Without A Telescope – Holographic Dark Information Energy

The bubble nebula NGC 7635 - it doesn't have a lot to do with Holographic Dark Information Energy, but you always have to start these articles with an image. Credit: Croman/APOD Nov 7 2005.

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Holographic Dark Information Energy gets my vote for the best mix of arcane theoretical concepts expressed in the shortest number of words – and just to keep it interesting, it’s mostly about entropy.

The second law of thermodynamics requires that the entropy of a closed system cannot decrease. So drop a chunk of ice in a hot bath and the second law requires that the ice melts and the bath water cools – moving the system from a state of thermal disequilibrium (low entropy) towards a state of thermal equilibrium (high entropy). In an isolated system (or an isolated bath) this process can only move in one direction and is irreversible.

A similar idea exists within information theory. Landauer’s principle has it that any logically irreversible manipulation of information, such as erasing one bit of information, equates to an increase in entropy.

So for example, if you keep photocopying the photocopy you just made of an image, the information in that image degrades and is eventually lost. But Landauer’s principle has it that the information is not so much lost, as converted into energy that is dissipated away by the irreversible act of copying a copy.

Translating this thinking into a cosmology, Gough proposes that as the universe expands and density declines, information-rich processes like star formation also decline. Or to put it in more conventional terms – as the universe expands, entropy increases since the energy density of the universe is being steadily dissipated across a greater volume. Also, there are less opportunities for gravity to generate low entropy processes like star formation.

The link between entropy and information - more interesting and information-rich things occur in low entropy states than in high entropy states.

So in an expanding universe there is a loss of information – and by Landauer’s principle this loss of information should release dissipated energy – and Gough claims that this dissipated energy accounts for the dark energy component of the current standard model of universe.

There are rational objections to this proposal. Landauer’s principle is really an expression of entropy in information systems – which can be mathematically modeled as though they were thermodynamic systems. It’s a bold claim to say this has a physical reality and a loss of information actually does release energy – and since Landauer’s principle expresses this as heat energy, wouldn’t it then be detectable (i.e. not dark)?

There is some experimental evidence of information loss releasing energy, but arguably it is just conversion of one form of energy to another – the information loss aspect of it just representing the transition from low to high entropy, as required by the second law of thermodynamics. Gough’s proposal requires that ‘new’ energy is introduced into the universe out of nowhere – although to be fair, that is pretty much what the current mainstream dark energy hypothesis requires as well.

Nonetheless, Gough alleges that the math of information energy does a much better job of accounting for dark energy than the traditional quantum vacuum energy hypothesis which predicts that there should be 120 orders of magnitude more dark energy in the universe than there apparently is.

Gough calculates that the information energy in the current era of the universe should be about 3 times its current mass-energy contents – which closely aligns with the current standard model of 74% dark energy + 26% everything else.

Invoking the holographic principle doesn’t add a lot to the physics of Gough’s argument – presumably it’s in there to make the math easier to manage by removing one dimension. The holographic principle has it that all the information about physical phenomena taking place within a 3D region of space can be contained on a 2D surface bounding that region of space. This, like information theory and entropy, is something that string theorists spend a lot of time grappling with – not that there’s anything wrong with that.

Further reading:
Gough Holographic Dark Information Energy.

Posted on by Jon Voisey

Examining the Great Wall

Several superclusters revealed by the 2dF Galaxy Redshift Survey. This contains the structure known as the "Sloan Great Wall". Courtesy 2dF Galaxy Redshift Survey.
Several superclusters revealed by the 2dF Galaxy Redshift Survey. This contains the structure known as the "Sloan Great Wall". Courtesy 2dF Galaxy Redshift Survey.

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Structure exists on nearly all scales in the universe. Matter clumps under its own gravity into planets, stars, galaxies, clusters, and superclusters. Beyond even these in scale are the filaments and voids. The largest of these filaments is known as the Sloan Great Wall. This giant string of galaxies is 1.4 billion light years across making it the largest known structure in the universe. Yet surprisingly, the Great Wall has never been studied in detail. Superclusters within it have been examined, but the wall as a whole has only come into consideration in a new paper from a team led by astronomers at Tartu Observatory in Estonia.

The Sloan Great Wall was first discovered in 2003 from the Sloan Digital Sky Survey (SDSS). The survey mapped the position of hundreds of millions of galaxies revealing the large scale structure of the universe and uncovering the Great Wall.

Within it, the wall contains several interesting superclusters. The largest of these SCl 126 has been shown previously to be unusual compared to superclusters within other large scale structures. SCl 126 is described as having an exceptionally rich core of galaxies with tendrils of galaxies trailing away from it like an enormous “spider”. Typical superclusters have many smaller clusters connected by these threads. This pattern is exemplified by one of the other rich superclusters in the wall, SCl 111. If the wall is examined in only its densest portions, the tendrils extending away from these cores are quite simple, but as the team explored lower densities, sub filaments became apparent.

Another way the team examined the Great Wall was by looking at the arrangement of different types of galaxies. In particular, the team looked for Bright Red Galaxies (BRGs) and found that these galaxies are often found together in groups with at least five BRGs present. These galaxies were often the brightest of the galaxies within their own groups. As a whole, the groups with BRGs tended to have more galaxies which were more luminous, and have a greater variety of velocities. The team suggests that this increased velocity dispersion is a result of a higher rate of interactions among galaxies than in other clusters. This is especially true for SCl 126 where many galaxies are actively merging. Within SCl 126, these BRG groups were evenly distributed between the core and the outskirts while in SCl 111, these groups tended to congregate towards the high density regions. In both of these superclusters, spiral galaxies comprised about 1/3 of the BRGs.

The study of such properties will help astronomers to test cosmological models that predict galactic structure formation. The authors note that models have generally done a good job of being able to account for structures similar to SCl 111 and most other superclusters we have observed in the universe. However, they fall short in creating superclusters with the size, morphology and distribution of SCl 126. These formations arise from density fluctuations initially present during the Big Bang. As such, understanding the structures they formed will help astronomers to understand these perturbations in greater detail and, in turn, what physics would be necessary to achieve them. To help achieve this, the authors intend to continue mapping the morphology of the Sloan Great Wall as well as other superclusters to compare their features.

Posted on by Nancy Atkinson

Gravity Probe B Confirms Two of Einstein’s Space-Time Theories

Einstein's predicted geodetic and frame-dragging effects, and the Schiff Equation for calculating them. Credit: Stanford University

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Researchers have confirmed two predictions of Albert Einstein’s general theory of relativity, concluding one of NASA’s longest-running projects. The Gravity Probe B experiment used four ultra-precise gyroscopes housed in an Earth-orbiting satellite to measure two aspects of Einstein’s theory about gravity. The first is the geodetic effect, or the warping of space and time around a gravitational body. The second is frame-dragging, which is the amount a spinning object pulls space and time with it as it rotates.

Gravity Probe-B determined both effects with unprecedented precision by pointing at a single star, IM Pegasi, while in a polar orbit around Earth. If gravity did not affect space and time, GP-B’s gyroscopes would point in the same direction forever while in orbit. But in confirmation of Einstein’s theories, the gyroscopes experienced measurable, minute changes in the direction of their spin, while Earth’s gravity pulled at them.

The project as been in the works for 52 years.

The findings are online in the journal Physical Review Letters.

Artist concept of Gravity Probe B orbiting the Earth to measure space-time, a four-dimensional description of the universe including height, width, length, and time. Image credit: NASA

“Imagine the Earth as if it were immersed in honey,”.said Francis Everitt, Gravity Probe-B principal investigator at Stanford University. “As the planet rotates, the honey around it would swirl, and it’s the same with space and time,” “GP-B confirmed two of the most profound predictions of Einstein’s universe, having far-reaching implications across astrophysics research. Likewise, the decades of technological innovation behind the mission will have a lasting legacy on Earth and in space.”

NASA began development of this project starting in the fall of 1963 with initial funding to develop a relativity gyroscope experiment. Subsequent decades of development led to groundbreaking technologies to control environmental disturbances on spacecraft, such as aerodynamic drag, magnetic fields and thermal variations. The mission’s star tracker and gyroscopes were the most precise ever designed and produced.

GP-B completed its data collection operations and was decommissioned in December 2010.

“The mission results will have a long-term impact on the work of theoretical physicists,” said Bill Danchi, senior astrophysicist and program scientist at NASA Headquarters in Washington. “Every future challenge to Einstein’s theories of general relativity will have to seek more precise measurements than the remarkable work GP-B accomplished.”

Innovations enabled by GP-B have been used in GPS technologies that allow airplanes to land unaided. Additional GP-B technologies were applied to NASA’s Cosmic Background Explorer mission, which accurately determined the universe’s background radiation. That measurement is the underpinning of the big-bang theory, and led to the Nobel Prize for NASA physicist John Mather.

The drag-free satellite concept pioneered by GP-B made a number of Earth-observing satellites possible, including NASA’s Gravity Recovery and Climate Experiment and the European Space Agency’s Gravity field and steady-state Ocean Circulation Explorer. These satellites provide the most precise measurements of the shape of the Earth, critical for precise navigation on land and sea, and understanding the relationship between ocean circulation and climate patterns.

GP-B also advanced the frontiers of knowledge and provided a practical training ground for 100 doctoral students and 15 master’s degree candidates at universities across the United States. More than 350 undergraduates and more than four dozen high school students also worked on the project with leading scientists and aerospace engineers from industry and government. One undergraduate student who worked on GP-B became the first female astronaut in space, Sally Ride. Another was Eric Cornell who won the Nobel Prize in Physics in 2001.

“GP-B adds to the knowledge base on relativity in important ways and its positive impact will be felt in the careers of students whose educations were enriched by the project,” said Ed Weiler, associate administrator for the Science Mission Directorate at NASA Headquarters.

Sources: NASA, Stanford University

Posted on by Jason Major

A New Spin on Galactic Evolution

Spiral galaxy arms may carry stars along with them, suggests new study

 

There’s a new concept in the works regarding the evolution of galactic arms and how they move across the structure of spiral galaxies. Robert Grand, a postgraduate student at University College London’s Mullard Space Science Laboratory, used new computer modeling to suggest that these signature features of spiral galaxies – including our own Milky Way – evolve in different ways than previously thought.

The currently accepted theory is as spiral galaxies rotate, the “arms” are actually transient structures that move across the flattened disc of stars surrounding the galactic bulge, yet don’t directly affect the movement of the individual stars themselves. This would work in much the same way as a “wave” goes across a crowd at a stadium event. The wave moves, but the individual people do not move along with it – rather, they stay seated after it has passed.

However when Grand researched this suggested motion using computer models of galaxies, he and his colleagues found that this was not what tended to happen. Instead the stars actually moved along with the arms, rather than maintaining their positions.

Also it was observed in these models that the arms themselves are not permanent features, but rather break up and reform over the course of 80 to 100 million years. Grand suggests that this may be due to the powerful gravitational shear forces generated by the spinning of the galaxy.

“We simulated the evolution of spiral arms for a galaxy with five million stars over a period of 6 billion years. We found that stars are able to migrate much more efficiently than anyone previously thought. The stars are trapped and move along the arm by their gravitational influence, but we think that eventually the arm breaks up due to the shear forces.”

– Robert Grand

Snapshots of face-on view of a simulated disc galaxy.

The computer models also showed that the stars along the leading edge of the arms tended to move inwards toward the galactic center while the stars lining the trailing ends were carried to the outer edge of the galaxy.

Since it takes hundreds of millions of years for a spiral galaxy to complete even just one single rotation, observing their evolution and morphology is impossible to do in real time. Researchers like Grand and his simulations are key to our eventual understanding of how these islands of stars formed and continue to shape themselves into the vast, varied structures we see today.

“This research has many potential implications for future observational astronomy, like the European Space Agency’s next corner stone mission, Gaia, which MSSL is also heavily involved in.  As well as helping us understand the evolution of our own galaxy, it may have applications for regions of star formation.”

– Robert Grand

The results were presented at the Royal Astronomical Society’s National Astronomy Meeting in Wales on April 20. Read the press release on the Royal Astronomical Society’s website here.

Top image: M81, a spiral galaxy similar to our own Milky Way, is one of the brightest galaxies that can be seen from Earth. The spiral arms wind all the way down into the nucleus and are made up of young, bluish, hot stars formed in the past few million years, while the central bulge contains older, redder stars. Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

Posted on by Nancy Atkinson

Early Stars Were Whirling Dervishes

Simulation of the formation of the first stars showing fast rotation. Credit: A. Stacy, University of Texas.

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Even though some of the first stars in the early universe were massive, they probably lived fast and furious lives, as they likely rotated much faster than their present-day counterparts. A new study on stellar evolution looked at a 12-billion-year-old star cluster and found high levels of metal in the stars – a chemical signature that suggests that the first stars were fast spinners.

“We think that the first generations of massive stars were very fast rotators – that’s why we called them spinstars,” said Cristina Chiappini of the Astrophysical Institute Potsdam in Germany, who led the team of astronomers.

These first generation stars died out long ago, and our telescopes can’t look back in time far enough to actually see them, but astronomers can get a glimpse of what they were like by looking at the chemical makeup of later stars. The first stars’ chemical imprints are like fossil records that can be found in the oldest stars we can study.

The general understanding of the early universe is that soon after the Big Bang, the Universe was made of essentially just hydrogen and helium. The chemical enrichment of the Universe with other elements had to wait around 300 million years until the fireworks started with the death of the first generations of massive stars, putting new chemical elements into the primordial gas, which later were incorporated in the next generations of stars.

Using data from ESO’s Very Large Telescope (VLT), the astronomers reanalyzed spectra of a group of very old stars in the Galactic Bulge. These stars are so old that only very massive, short-living stars with masses larger than around ten times the mass of our Sun should have had time to die and to pollute the gas from which these fossil records then formed. As expected, the chemical composition of the observed stars showed elements typical for enrichment by massive stars. However, the new analysis unexpectedly also revealed elements usually thought to be produced only by stars of smaller masses. Fast-rotating massive stars on the other hand would succeed in manufacturing these elements themselves.

“Alternative scenarios cannot yet be discarded – but – we show that if the first generations of massive stars were spinstars, this would offer a very elegant explanation to this puzzle!” said Chiappini.

A star that spins more rapidly can live longer and suffer different fates than slow-spinning ones. Fast rotation also affects other properties of a star, such as its colour, and its luminosity. Spinstars would therefore also have strongly influenced the properties and appearance of the first galaxies which were formed in the Universe. The existence of spinstars is now also supported by recent hydrodynamic simulations of the formation of the first stars of the universe by an independent research group.

Chiappini and her team are currently working on extending the stellar simulations in order to further test their findings. Their work is published in a Nature article on April 28, 2011.

Source: University of Potsdam, Nature

Posted on by Nancy Atkinson

Did the Early Universe Have Just One Dimension?

Planck all-sky image. Credit: ESA, HFI and LFI consortia.

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From a University of Buffalo press release:

Did the early universe have just one spatial dimension? That’s the mind-boggling concept at the heart of a theory that physicist Dejan Stojkovic from the University at Buffalo and colleagues proposed in 2010. They suggested that the early universe — which exploded from a single point and was very, very small at first — was one-dimensional (like a straight line) before expanding to include two dimensions (like a plane) and then three (like the world in which we live today).

The theory, if valid, would address important problems in particle physics.

Now, in a new paper in Physical Review Letters, Stojkovic and Loyola Marymount University physicist Jonas Mureika describe a test that could prove or disprove the “vanishing dimensions” hypothesis.

Because it takes time for light and other waves to travel to Earth, telescopes peering out into space can, essentially, look back into time as they probe the universe’s outer reaches.

Gravitational waves can’t exist in one- or two-dimensional space. So Stojkovic and Mureika have reasoned that the Laser Interferometer Space Antenna (LISA), a planned international gravitational observatory, should not detect any gravitational waves emanating from the lower-dimensional epochs of the early universe.

Stojkovic, an assistant professor of physics, says the theory of evolving dimensions represents a radical shift from the way we think about the cosmos — about how our universe came to be.

The core idea is that the dimensionality of space depends on the size of the space we’re observing, with smaller spaces associated with fewer dimensions. That means that a fourth dimension will open up — if it hasn’t already — as the universe continues to expand.

The theory also suggests that space has fewer dimensions at very high energies of the kind associated with the early, post-big bang universe.

If Stojkovic and his colleagues are right, they will be helping to address fundamental problems with the standard model of particle physics, including the following:

The incompatibility between quantum mechanics and general relativity. Quantum mechanics and general relativity are mathematical frameworks that describe the physics of the universe. Quantum mechanics is good at describing the universe at very small scales, while relativity is good at describing the universe at large scales. Currently, the two theories are considered incompatible; but if the universe, at its smallest levels, had fewer dimensions, mathematical discrepancies between the two frameworks would disappear.

Physicists have observed that the expansion of the universe is speeding up, and they don’t know why. The addition of new dimensions as the universe grows would explain this acceleration. (Stojkovic says a fourth dimension may have already opened at large, cosmological scales.)

The standard model of particle physics predicts the existence of an as yet undiscovered elementary particle called the Higgs boson. For equations in the standard model to accurately describe the observed physics of the real world, however, researchers must artificially adjust the mass of the Higgs boson for interactions between particles that take place at high energies. If space has fewer dimensions at high energies, the need for this kind of “tuning” disappears.

“What we’re proposing here is a shift in paradigm,” Stojkovic said. “Physicists have struggled with the same problems for 10, 20, 30 years, and straight-forward extensions of the existing ideas are unlikely to solve them.”

“We have to take into account the possibility that something is systematically wrong with our ideas,” he continued. “We need something radical and new, and this is something radical and new.”

Because the planned deployment of LISA is still years away, it may be a long time before Stojkovic and his colleagues are able to test their ideas this way.

However, some experimental evidence already points to the possible existence of lower-dimensional space.

Specifically, scientists have observed that the main energy flux of cosmic ray particles with energies exceeding 1 teraelectron volt — the kind of high energy associated with the very early universe — are aligned along a two-dimensional plane.

If high energies do correspond with lower-dimensional space, as the “vanishing dimensions” theory proposes, researchers working with the Large Hadron Collider particle accelerator in Europe should see planar scattering at such energies.

Stojkovic says the observation of such events would be “a very exciting, independent test of our proposed ideas.”

Sources: EurekAlert, Physical Review Letters.