Space and astronomy news
Some of the biggest questions in the universe depend on its shape. Is it curved? Is it flat? Is it open? Those may not make that much sense to you, but in fact it’s very important for astronomers. So which is it? How do we know? How did we figure it out? Why does it matter?
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What is the shape of the Universe? – Show notes and transcript
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So how do rare massive stars grow 10 to 150 times the mass of our Sun? It turns out that a standard star-forming nebula is way too cold for big stars to form. So how can these clouds of gas and dust be prepared so massive stars can develop? Answer: Let small stars do the hard work and heat that nebula up…
This is the ultimate stellar crèche. Star-forming nebulae are vast regions of space filled with gas and dust. Proto-stars need a lot of hydrogen to form and begin fusion reactions in their young cores. The bigger the nebula, the bigger the star… or so you’d think.
The problem with these young nebulae is that they are cold; in fact they are very cold. Typical interstellar clouds of hydrogen have temperatures very close to absolute zero (the lowest temperature possible) due to the lack of heat in the far-off reaches of the cosmos. Cold clouds will fragment very easily, breaking up and forming smaller clouds of hydrogen. Eventually they will collapse to form stars, but these stars will be very small due to the lack of fuel in the nebula fragment. If this is the case, how are massive stars – the ones responsible for producing heavy elements including anything heavier than helium – formed at all? Surely all clouds of dust and gas are cold, and therefore fragment, only producing small stars?
From research published in Nature this weekby Christopher F. McKee (a professor from UC Berkeley) and Mark R. Krumholz (Hubble postdoctoral fellow at Princeton), there is a possible solution to this problem. Perhaps young stars provide a heating source to warm up the surrounding nebula, preventing the surrounding gas from fragmenting, allowing it to collapse into progressively bigger stars.
Starting at temperatures only 10-20 degrees above absolute zero, clouds heated by young stars may increase in temperatures three-fold. However, researchers realize that a massive star-forming cloud needs to be several hundred degrees warmer than absolute zero to prevent the whole cloud from fragmenting, they also understand that the “zone of heating” for each small star is limited in less dense clouds. This situation changes when the star-forming cloud is dense. The zone of influence each small star has will encompass the whole nebula. This collaborative heating effect by the small stars prevents fragmentation and allows larger volumes of gas to collapse, forming massive stars.
“It’s only the formation of these low-mass stars that heats up the cloud enough to cut off the fragmentation. It is as if the cold molecular cloud starts on the process of making low-mass stars but then, because of heating, that fragmentation is stopped and the rest of the gas goes into one large star.” – Christopher F. McKee.
A warmer cloud is a bigger cloud, providing more fuel, allowing massive stars to form. It is the ultimate stellar nursery; massive stars can only form once their smaller (and older) siblings warm up the cosmic nest for them to thrive.
View the stunning simulation of a massive star forming in a warm cloud (24Mb, .mpg)
Source: UC Berkley News
There are some people – I’m not naming names – who think the universe revolves around them. In fact, for most of humankind, everybody thought that. It’s only been in the last few hundred years that scientists finally puzzled out that the Earth isn’t the centre of the universe at all. That begs the question: where is the centre?
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Where is the Centre of the Universe? – Show notes and transcript
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Pulsars are fast-spinning, highly radiating neutron stars. Most pulsars emit radio, X-ray and gamma radiation at regular intervals (usually periods of a few milliseconds to a few seconds), in fact many pulses keep the accuracy of the most accurate atomic clocks on Earth. However, occasionally, these rapidly rotating bodies undergo a violent change, blasting massive quantities of energy into space. Although short-lived (a fraction of a second), the observed explosion packs a punch of at least 75,000 Suns. Is this a natural process in the life of a pulsar? Is it a totally different type of cosmic phenomena? Researchers suggest these observations may be a different type of neutron star: magnetars disguised as pulsars (and without an ounce of dark matter in sight!)…
Neutron stars are a product of massive stars after a supernova. The star isn’t big enough to create a black hole (i.e. less than 5 solar masses), but it is big enough to create a tiny, dense and hot mass of neutrons (hence the name). Due to the “Pauli exclusion principal” – a quantum mechanical principal that prevents any two neutrons from having the same quantum characteristics within the same volume – neutron stars are also predicted to be very hot. Intense gravity forces matter into a tiny volume, but quantum effects are repelling the neutrons. After the star has gone supernova, as neutron stars are so small (a radius of only 10 to 20 km), the small mass preserves the stars angular momentum, resulting in a fast-spinning, highly radiating body.
Much of the stars magnetism is also preserved, but in a vastly increased dense state. Neutron stars are therefore expected to have an intense magnetic field. It is in fact this magnetic field that helps to generate jets of emission from the magnetic poles of the rotating body, creating a beam of radiation (much like a lighthouse).
However, one of these flashing lighthouses has surprised observers… it exploded, blasting vast amounts of energy into space, and then continued to spin and flash as if nothing had happened. This phenomenon has recently been observed by NASA’s Rossi X-ray Timing Explorer (RXTE) and has been backed up by data from the Chandra X-ray Observatory.
There are in fact other classes of neutron star out there. Slow-spinning, highly magnetic “magnetars” are considered to be a separate type of neutron star. They are distinct from the less-magnetic pulsar as they sporadically release vast amounts of energy into space and do not exhibit the periodic rotation we understand from pulsars. It is believed that magnetars explode as the intense magnetic field (the strongest magnetic field believed to exist in the Universe) warps the neutron star surface, causing extremely energetic reconnection events between magnetic flux, causing violent and sporadic X-ray bursts.
There is now speculation that known periodic pulsars that suddenly exhibit magnetar-like explosions are actually the highly magnetic cousins of pulsars disguised as pulsars. Pulsars simply do not have enough magnetic energy to generate explosions of this magnitude, magnetars do.
Fotis Gavriil of NASA’s Goddard Space Flight Center in Greenbelt, and his colleagues analysed a young neutron star (called PSR J1846-0258 in the constellation Aquila). This pulsar was often considered to be “normal” due to its fast spin (3.1 revolutions per second), but RXTE observed five magnetar-like X-ray bursts from the pulsar in 2006. Each event lasted no longer than 0.14 seconds and generated the energy of 75,000 Suns. Follow up observations by Chandra confirmed that over the course of six years, the pulsar had become more “magnetar-like”. The rotation of the pulsar is also slowing down, suggesting a high magnetic field may be braking its rotation.
These findings are significant, as it suggests that pulsars and magnetars may be the same creature, just at different periods of a pulsars lifetime, and not two entirely different classes of neutron star…
Results of this research will be published in today’s issue of Science Express.
Source: AAAS Science Express
I’ve said it many times, but it bears repeating: regular matter only accounts for 4% of the Universe. The other 96% – dark matter and dark energy – is a total mystery. Wouldn’t it be convenient if we could find a single explanation for both? Astronomers from the University of St. Andrews are ready to decrease the mysteries down to one.
Dr. HongSheng Zhao at the University of St. Andrews School of Physics and Astronomy has developed a model that shows how dark energy and dark matter are more closely linked than previously thought.
Dr Zhao points out, “Both dark matter and dark energy could be two faces of the same coin. “As astronomers gain understanding of the subtle effects of dark energy in galaxies in the future, we will solve the mystery of astronomical dark matter at the same time.”
Just a quick explainer. Dark energy was discovered in the late 1990s during a survey of distant supernova. Instead of finding evidence that the mutual gravity of all the objects in the Universe is slowing down its expansion, researchers discovered that its expansion is actually accellerating.
Dark matter was first theorized back in 1933 by Swiss astronomer Fritz Zwicky. He noted that galaxies shouldn’t be able to hold themselves together with just the regular matter we can see. There must be some additional, invisible matter surrounding the regular matter that provides the additional gravitational force to hold everything together.
And since their discoveries plenty of additional evidence for both dark energy and dark matter have been seen across the Universe.
In Dr. Zhao’s model, dark energy and dark matter the same thing that he calls a “dark fluid”. On the scale of galaxies, this fluid behaves like matter, providing a gravitational force. And in the large scales, the fluid helps drive the expansion of the Universe.
Dr. Zhao’s model is detailed enough to produce the same 3:1 ratio of dark energy to dark matter measured by cosmologists.
Of course, any theory like this only gains ground when it starts making predictions that can be tested through observation. Dr. Zhao expects the work at the Large Hadron Collider to be fruitless. If he’s right, dark matter particles will have such low energy that the collider won’t be able to generate them.
The paper was recently published in the Astrophysical Journal Letters in December 2007, and Physics Review D. 2007.
Original Source: University of St. Andrews News Release
What is the universe made of? While general relativity does a good job providing insights into the Big Bang and the evolution of stars, galaxies and black holes, the theory doesn’t help much when it gets down to the small stuff. There are several theories about the basic, fundamental building blocks of all that exists. Some quantum physicists propose string theory as a theory of “everything,” that at the elemental heart of all matter lie tiny one-dimensional filaments called strings. Unfortunately, however, according to the theory, strings should be about a millionth of a billionth of a billionth of a billionth of a centimeter in length. Strings are way too small to see with current particle physics technology, so string theorists will have to come up with more clever methods to test the theory than just looking for the strings.
Well, one cosmologist has an idea. And it’s a really big idea.
Benjamin Wandelt, a professor of physics and astronomy at the University of Illinois says that ancient light from the beginnings of our universe was absorbed by neutral hydrogen atoms. By studying these atoms, certain predictions of string theory could be tested. Making the measurements, however, would require a gigantic array of radio telescopes to be built on Earth, in space or on the moon. And it would be really gigantic: Wandelt proposes an array of radio telescopes with a collective area of more than 1,000 square kilometers. Such an array could be built using current technology, Wandelt said, but would be prohibitively expensive.
So for now, both string theory and this method of testing are purely hypothetical.
According to Wandelt, what this huge array would be looking for are absorption features in the 21-centimeter spectrum of neutral hydrogen atoms.
“High-redshift, 21-centimeter observations provide a rare observational window in which to test string theory, constrain its parameters and show whether or not it makes sense to embed a type of inflation — called brane inflation– into string theory,” said Wandelt. “If we embed brane inflation into string theory, a network of cosmic strings is predicted to form. We can test this prediction by looking for the impact this cosmic string network would have on the density of neutral hydrogen in the universe.”
About 400,000 years after the Big Bang, the universe consisted of a thick shell of neutral hydrogen atoms (each composed of a single proton orbited by a single electron) illuminated by what became known as the cosmic microwave background.
Because neutral hydrogen atoms readily absorb electromagnetic radiation with a wavelength of 21 centimeters, the cosmic microwave background carries a signature of density perturbations in the hydrogen shell, which should be observable today, Wandelt said.
Cosmic strings are filaments of infinite length. Wandelt compared their composition to the boundaries of ice crystals in frozen water.
When water in a bowl begins to freeze, ice crystals will grow at different points in the bowl, with random orientations. When the ice crystals meet, they usually will not be aligned to one another. The boundary between two such misaligned crystals is called a discontinuity or a defect.
Cosmic strings are defects in space. String theory predicts that a network of strings were produced in the early universe, but this has not been detected so far. Cosmic strings produce fluctuations in the gas density through which they move, a signature of which Wandelt says will be imprinted on the 21-centimeter radiation.
Like the cosmic microwave background, the cosmological 21-centimeter radiation has been stretched as the universe has expanded. Today, this relic radiation has a wavelength closer to 21 meters, putting it in the long-wavelength radio portion of the electromagnetic spectrum.
If such an enormous array were eventually constructed, measurements of perturbations in the density of neutral hydrogen atoms could also reveal the value of string tension, a fundamental parameter in string theory, Wandelt said. “And that would tell us about the energy scale at which quantum gravity begins to become important.”
But questions remain about the validity of this experiment. Also, could the array somehow be “shrunk” to search only a small area of the 21-centimeter radiation? Or possibily, could an instrument similar to WMAP (Wilkinson Microwave Anisotropy Probe) be constructed to look at the entire sky for this radiation?
Wandelt and graduate student Rishi Khatri describe their proposed test in a paper accepted for publication in the journal Physical Review Letters, and the paper is not yet available for public review.
Original News Source: University of Illinois Press Release
What if time disappeared? Yes, it sounds like a silly question – and if the cosmos sticks to the current laws of physics – it’s a question we need never ask beyond this article. Writing this article would in itself be a waste of my time if the cosmos was that simple. But I’m hedging my bets and continuing to type, as I believe we have only just scratched the surface of the universal laws of physics; the universe is anything but simple. There may in fact be something to this crazy notion that the nature of the universe could be turned on its head should the fundamental quantity of time be transformed into another dimension of space. An idea like this falls out of the domain of classical thought, and into the realms of “braneworlds”, a view that encapsulates the 4-dimensional universe we know and love with superstrings threaded straight through…
Brane theory is a strange idea. In a nutshell, a brane (short for “membrane”) can be viewed as a sheet floating in a fifth dimension. As we can only experience three dimensional space along one dimension of time (four dimensional space-time, a.k.a. a Lorentzian universe), we cannot understand what this fifth dimension looks like, but we are fortunate to have mathematics to help us out. Mathematics can be used to describe as many dimensions as we like. Useful, as branes describe the cumulative effect of “strings” threading through many dimensions and the forces interacting to create the universe we observe in boring old three dimensional space. According to the “braneworld” view, our four dimensional cosmos may actually be embedded within a multidimensional universe – our cosmic version only uses four of the many possible dimensions.
Theorists contemplating braneworlds, such as Marc Mars at the University of Salamanca in Spain, now believe they have stumbled on an implication that could, quite literally, stop cosmologists in their tracks. The time dimension could soon be disappearing to be replaced by a fourth space dimension. Our familiar Lorentzian universe could turn Euclidean (i.e. four spatial dimensions, no time) and Mars believes the evidence for the change is staring us in the face.
“One of the interesting, and intriguing, properties of these signature-changing branes is that, even though the change of signature may be conceived as a dramatical event within the brane, both the bulk and the brane can be fully smooth. In particular, observers living in the brane but assuming that their Universe is Lorentzian everywhere may be misled to interpret that a curvature singularity arises precisely at the signature change” – Marc Mars, from Is the accelerated expansion evidence of a forthcoming change of signature on the brane?.
The observed expansion of the universe (as discovered by Edwin Hubble in 1925) may in fact be a symptom of a “signature changing” brane. If our brane is mutating from time-like to space-like, observers in the Lorentzian universe should observe an expanding and accelerating universe, exactly as we are observing presently. Mars goes on to detail that this theory can explain this ever increasing expansion, whilst keeping the physical characteristics of the cosmos as we observe today, without assuming any form of dark matter or dark energy is responsible.
It is doubtful that we can ever perceive a time-less cosmos, and what would happen to the universe should time go space-like is beyond our comprehension. So, enjoy your four dimensions while they last, time could soon be running out.
Source: arXiv blog
I know, I know, you’re probably getting sick of hearing this. Astronomers have no idea what 95% of the Universe is; 70% is dark energy, and 25% is dark matter, leaving a mere 5% normal matter. But it gets worse. Astronomers can only actually account for about 60% of that regular matter (hydrogen, helium and heavier elements) – almost half of the regular matter is missing too!
I’ll repeat that, just so it’s clear. Of the 5% of the Universe that we can even understand, almost half of it is missing too.
Researchers at the University of Colorado at Boulder have used a powerful supercomputer at the San Diego Supercomputing Center to try and figure out where this missing mass could be hiding, and they think they’ve got a good place to look.
They built up a simulation of a huge chunk of Universe, 1.5 billion light-years on a side. Within this simulated Universe, they saw that much of the gas in the Universe forms into a tangled web of filaments that stretch for hundreds of million of light-years. In between these filaments are vast spherical voids without any matter.
The simulation works by modeling how material came together through gravity after the Big Bang. The simulation predicts that this missing material is hiding within gas clouds called the Warm-Hot Intergalactic Medium.
If their predictions are correct, the next generation of telescopes should be able to detect this missing mass in these hidden filaments. Some of these telescopes include the 10-metre South Pole Telescope in Antarctica and the 25-metre Cornell-Caltech Atacama Telescope (CCAT).
The South Pole Telescope will look at how the Cosmic Microwave Background Radiation is heated up as it passes through clouds of this gas. CCAT will be able to look back to periods just after the Big Bang, and see how the first large scale structures started to come together.
At least then, we’ll probably know where all that 5% of regular mass is. Dark matter and dark energy? Still a mystery.
Original Source: CU-Boulder News Release
It’s about time for a question show again, so we’ll have one last interruption to our planetary tour, to deal with the questions that arose from our inflation show. So if you still don’t understand inflation, take a listen to this week’s show and as always, send us your questions.
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Questions on Inflation – Show notes and transcript
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We interrupt this tour through the Solar System to bring you a special show to deal with one of our most complicated subjects: the Big Bang. Specifically, how it’s possible that the universe could have expanded faster than the speed of light. The theory is called the inflationary theory, and the evidence is mounting to support it. Einstein said that nothing can move faster than the speed of light, and yet astronomers think the universe expanded from a microscopic spec to become larger than the solar system, in a fraction of a second.
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Inflation – Show notes and transcript
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