Posts Tagged ‘Supernovae

Birth of a black hole?

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A new kind of cosmic flash may reveal something never seen before: the birth of a black hole.


Credit: Alain Riazuelo, IAP/UPMC/CNRS

When a massive star exhausts its fuel, it collapses under its own gravity and produces a black hole, an object so dense that not even light can escape its gravitational grip. According to a new analysis by an astrophysicist at the California Institute of Technology (Caltech), just before the black hole forms, the dying star may generate a distinct burst of light that will allow astronomers to witness the birth of a new black hole for the first time.

Tony Piro, a postdoctoral scholar at Caltech, describes this signature light burst in a paper published in the May 1 issue of the Astrophysical Journal Letters. While some dying stars that result in black holes explode as gamma-ray bursts, which are among the most energetic phenomena in the universe, those cases are rare, requiring exotic circumstances, Piro explains. “We don’t think most run-of-the-mill black holes are created that way.” In most cases, according to one hypothesis, a dying star produces a black hole without a bang or a flash: the star would seemingly vanish from the sky—an event dubbed an unnova. “You don’t see a burst,” he says. “You see a disappearance.”

But, Piro hypothesizes, that may not be the case. “Maybe they’re not as boring as we thought,” he says.

According to well-established theory, when a massive star dies, its core collapses under its own weight. As it collapses, the protons and electrons that make up the core merge and produce neutrons. For a few seconds—before it ultimately collapses into a black hole—the core becomes an extremely dense object called a neutron star, which is as dense as the sun would be if squeezed into a sphere with a radius of about 10 kilometers (roughly 6 miles). This collapsing process also creates neutrinos, which are particles that zip through almost all matter at nearly the speed of light. As the neutrinos stream out from the core, they carry away a lot of energy—representing about a tenth of the sun’s mass (since energy and mass are equivalent, per E = mc2).

According to a little-known paper written in 1980 by Dmitry Nadezhin of the Alikhanov Institute for Theoretical and Experimental Physics in Russia, this rapid loss of mass means that the gravitational strength of the dying star’s core would abruptly drop. When that happens, the outer gaseous layers—mainly hydrogen—still surrounding the core would rush outward, generating a shock wave that would hurtle through the outer layers at about 1,000 kilometers per second (more than 2 million miles per hour).

Using computer simulations, two astronomers at UC Santa Cruz, Elizabeth Lovegrove and Stan Woosley, recently found that when the shock wave strikes the outer surface of the gaseous layers, it would heat the gas at the surface, producing a glow that would shine for about a year—a potentially promising signal of a black-hole birth. Although about a million times brighter than the sun, this glow would be relatively dim compared to other stars. “It would be hard to see, even in galaxies that are relatively close to us,” says Piro.

But now Piro says he has found a more promising signal. In his new study, he examines in more detail what might happen at the moment when the shock wave hits the star’s surface, and he calculates that the impact itself would make a flash 10 to 100 times brighter than the glow predicted by Lovegrove and Woosley. “That flash is going to be very bright, and it gives us the best chance for actually observing that this event occurred,” Piro explains. “This is what you really want to look for.”

Such a flash would be dim compared to exploding stars called supernovae, for example, but it would be luminous enough to be detectable in nearby galaxies, he says. The flash, which would shine for 3 to 10 days before fading, would be very bright in optical wavelengths—and at its very brightest in ultraviolet wavelengths.

Piro estimates that astronomers should be able to see one of these events per year on average. Surveys that watch the skies for flashes of light like supernovae—surveys such as the Palomar Transient Factory (PTF), led by Caltech—are well suited to discover these unique events, he says. The intermediate Palomar Transient Factory (iPTF), which improves on the PTF and just began surveying in February, may be able to find a couple of these events per year.

Neither survey has observed any black-hole flashes as of yet, says Piro, but that does not rule out their existence. “Eventually we’re going to start getting worried if we don’t find these things.” But for now, he says, his expectations are perfectly sound.

With Piro’s analysis in hand, astronomers should be able to design and fine-tune additional surveys to maximize their chances of witnessing a black-hole birth in the near future. In 2015, the next generation of PTF, called the Zwicky Transient Facility (ZTF), is slated to begin; it will be even more sensitive, improving by several times the chances of finding those flashes. “Caltech is therefore really well-positioned to look for transient events like this,” Piro says.

Within the next decade, the Large Synoptic Survey Telescope (LSST) will begin a massive survey of the entire night sky. “If LSST isn’t regularly seeing these kinds of events, then that’s going to tell us that maybe there’s something wrong with this picture, or that black-hole formation is much rarer than we thought,” he says.

The Astrophysical Journal Letters paper is titled “Taking the ‘un’ out of unnovae.” This research was supported by the National Science Foundation, NASA, and the Sherman Fairchild Foundation.

Written by Marcus Woo –

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May 4, 2013 at 10:42 am


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Most ancient supernovas discovered

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One of ten supernovas in the Subaru Deep Field, which exploded 10 billion years ago. Credit: Image courtesy of Tel Aviv University

Supernovas — stars in the process of exploding — open a window onto the history of the elements of Earth’s periodic table as well as the history of the universe. All of those heavier than oxygen were formed in nuclear reactions that occurred during these explosions.

The most ancient explosions, far enough away that their light is reaching us only now, can be difficult to spot. A project spearheaded by Tel Aviv University researchers has uncovered a record-breaking number of supernovas in the Subaru Deep Field, a patch of sky the size of a full moon. Out of the 150 supernovas observed, 12 were among the most distant and ancient ever seen.

The discovery sharpens our understanding of the nature of supernovas and their role in element formation, say study leaders Prof. Dan Maoz, Dr. Dovi Poznanski and Or Graur of TAU’s Department of Astrophysics at the Raymond and Beverly Sackler School of Physics and Astronomy. These “thermonuclear” supernovas in particular are a major source of iron in the universe.

The research, which appears in the  this month, was done in collaboration with teams from a number of Japanese and American institutions, including the University of Tokyo, Kyoto University, the University of California Berkeley, and Lawrence Berkeley National Laboratory.

A key element of the universe

Supernovas are nature’s “element factories.” During these explosions, elements are both formed and flung into interstellar space, where they serve as raw materials for new generations of stars and planets. Closer to home, says Prof. Maoz, “these elements are the atoms that form the ground we stand on, our bodies, and the iron in the blood that flows through our veins.” By tracking the frequency and types of supernova explosions back through cosmic time, astronomers can reconstruct the universe’s history of element creation.

In order to observe the 150,000 galaxies of the Subaru Deep Field, the team used the Japanese Subaru Telescope in Hawaii, on the 14,000-foot summit of the extinct Mauna Kea volcano. The telescope’s light-collecting power, sharp images, and wide field of view allowed the researchers to overcome the challenge of viewing such distant supernovas.

By “staring” with the telescope at the Subaru Deep Field, the faint light of the most distant galaxies and supernovas accumulated over several nights at a time, forming a long and deep exposure of the field. Over the course of observations, the team “caught” the supernovas in the act of exploding, identifying 150 supernovas in all.

Sourcing man’s life-blood

According to the team’s analysis, thermonuclear type supernovas, also called Type-la, were exploding about five times more frequently 10 billion years ago than they are today. These supernovas are a major source of iron in the universe, the main component of the Earth’s core and an essential ingredient of the blood in our bodies.

Scientists have long been aware of the “universal expansion,” the fact that galaxies are receding from one another. Observations using Type-Ia supernovas as beacons have shown that the expansion is accelerating, apparently under the influence of a mysterious “dark energy” — the 2011 Nobel Prize in Physics will be awarded to three astronomers for this work. However, the nature of the supernovas themselves is poorly understood. This study improves our understanding by revealing the range of the ages of the stars that explode as Type-la supernovas. Eventually, this will enhance their usefulness for studying dark energy and the universal expansion, the researchers explain.

Provided by Tel Aviv University

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October 5, 2011 at 9:31 am


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Hubble Space Telescope Contributes to Nobel Prize in Physics

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These snapshots, taken by NASA's Hubble Space Telescope, reveal five supernovae, or exploding stars, and their host galaxies. The arrows in the top row of images point to the supernovae. The bottom row shows the host galaxies before or after the stars exploded. The supernovae exploded between 3.5 and 10 billion years ago.

Observations made by NASA’s Hubble Space Telescope of a special type of supernovae contributed to research on the expansion of the universe that today was honored with the 2011 Nobel Prize in Physics.

Adam Riess, an astronomer at the Space Telescope Science Institute and Krieger-Eisenhower professor in physics and astronomy at The Johns Hopkins University in Baltimore, was a member of a team awarded the Nobel Prize in Physics by the Royal Swedish Academy of Sciences. The academy recognized him for leadership in the High-z Team’s 1998 discovery that the expansion rate of the universe is accelerating, a phenomenon widely attributed to a mysterious, unexplained “dark energy” filling the universe. Critical parts of the work were done with NASA’s Hubble Space Telescope.

Riess shares the prize with Saul Perlmutter, an astrophysicist at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory, whose Supernova Cosmology Project team published similar results shortly after those published by Riess and High-z teammate Brian Schmidt of the Australian National University. Both teams shared the Peter Gruber Foundation’s 2007 Cosmology Prize — a gold medal and $500,000 — for the discovery of dark energy, which Science Magazine called “The Breakthrough Discovery of the Year” in 1998.

“The work of Reiss and others has completely transformed our understanding of the universe,” said Waleed Abdalati, NASA chief scientist. “This award also recognizes the tremendous contributions of the technological community that engineered, deployed, and serviced the Hubble Space Telescope, which continues to open new doors to discovery after more than 20 years of peering deep into the universe. With the future launch of the even more powerful James Webb Space Telescope, NASA is ensuring more revolutionary science discoveries like these in our future.”

Space Telescope Science Institute director Matt Mountain added, “The power of this discovery is that NASA has kept Hubble going for 20 years. This meant that Adam was able to track the history of the universe using science instruments that were upgraded from one servicing mission to the next. That is why this work has been recognized with the Nobel Prize.”

Riess led the study for the High-z Supernova Search Team of highly difficult and precise measurements of objects that spanned 7 billion light years that resulted in the 1998 discovery that many believe has changed astrophysics forever: an accelerated expansion of the universe propelled by dark energy….. Read the rest of this entry »

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October 4, 2011 at 10:00 pm

Supernovae, Dark Energy, and the Accelerating Universe

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Using very distant supernovae as standard candles, one can trace the history of cosmic expansion and try to find out what’s currently speeding it up.

Saul Perlmutter

 For millennia, cosmology has been a theorist’s domain, where elegant theory was only occasionally endangered by inconvenient facts. Early in the 20th century, Albert Einstein gave us new conceptual tools to rigorously address the questions of the origins, evolution, and fate of the universe. In recent years, technology has developed to the point where these concepts from general relativity can be substantiated and elaborated by measurements. For example, measurement of the remnant glow from the hot, dense beginnings of the expanding universe–the cosmic microwave background–is yielding increasingly detailed data about the first half-million years and the overall geometry of the cosmos (see the news story on page 21 of this issue).

The standard model of particle physics has also begun to play a prominent role in cosmology. The widely accepted idea of exponential inflation in the immediate aftermath of the Big Bang was built on the predicted effect of certain putative particle fields and potentials on the cosmic expansion. Measuring the history of cosmic expansion is no easy task, but in recent years, a specific variety of supernovae, type Ia, has given us a first glimpse at that history–and surprised us with an unexpected plot twist.

Searching for a standard candle

In principle, the expansion history of the cosmos can be determined quite easily, using as a “standard candle” any distinguishable class of astronomical objects of known intrinsic brightness that can be identified over a wide distance range. As the light from such beacons travels to Earth through an expanding universe, the cosmic expansion stretches not only the distances between galaxy clusters, but also the very wavelengths of the photons en route. By the time the light reaches us, the spectral wavelength λ has thus been redshifted by precisely the same incremental factor z ≡ Δλ/λ by which the cosmos has been stretched in the time interval since the light left its source. That time interval is the speed of light times the object’s distance from Earth, which can be determined by comparing its apparent brightness to a nearby standard of the same class of astrophysical objects.

The recorded redshift and brightness of each such object thus provide a measurement of the total integrated expansion of the universe since the time the light was emitted. A collection of such measurements, over a sufficient range of distances, would yield an entire historical record of the universe’s expansion.

Conceptually, this scheme is a remarkably straightforward means to a profound prize: an empirical account of the growth of our universe. A spectroscopically distinguishable class of objects with determinable intrinsic brightness would do the trick. In Edwin Hubble’s discovery of the cosmic expansion in the 1920s, he used entire galaxies as standard candles. But galaxies, coming in many shapes and sizes, are difficult to match against a standard brightness. They can grow fainter with time, or brighter–by merging with other galaxies. In the 1970s, it was suggested that the brightest member of a galaxy cluster might serve as a reliable standard candle. But in the end, all proposed distant galactic candidates were too susceptible to evolutionary change.

As early as 1938, Walter Baade, working closely with Fritz Zwicky, pointed out that supernovae were extremely promising candidates for measuring the cosmic expansion. Their peak brightness seemed to be quite uniform, and they were bright enough to be seen at extremely large distances.1 In fact, a supernova can, for a few weeks, be as bright as an entire galaxy. Over the years, however, as more and more supernovae were measured, it became clear that they were a rather heterogeneous group with a wide range of intrinsic peak brightnesses.

In the early 1980s, a new subclassification of supernovae emerged. Supernovae with no hydrogen features in their spectra had previously all been classified simply as type I. Now this class was subdivided into types Ia and Ib, depending on the presence or absence of a silicon absorption feature at 6150 Å in the supernova’s spectrum.2 With that minor improvement in typology, an amazing consistency among the type Ia supernovae became evident. Their spectra matched feature-by-feature, as did their “light curves”–the plots of waxing and waning brightness in the weeks following a supernova explosion.3,4

The uniformity of the type Ia supernovae became even more striking when their spectra were studied in detail as they brightened and then faded. First, the outermost parts of the exploding star emit a spectrum that’s the same for all typical type Ia supernovae, indicating the same elemental densities, excitation states, velocities, and so forth. Then, as the exploding ball of gas expands, the outermost layers thin out and become transparent, letting us see the spectral signatures of conditions further inside. Eventually, if we watch the entire time series of spectra, we get to see indicators that probe almost the entire explosive event. It is impressive that the type Ia supernovae exhibit so much uniformity down to this level of detail. Such a “supernova CAT-scan” can be difficult to interpret. But it’s clear that essentially the same physical processes are occurring in all of these explosions.

The detailed uniformity of the type Ia supernovae implies that they must have some common triggering mechanism . Equally important, this uniformity provides standard spectral and light-curve templates that offer the possibility of singling out those supernovae that deviate slightly from the norm. The complex natural histories of galaxies had made them difficult to standardize. With type Ia supernovae, however, we saw the chance to avoid such problems. We could examine the rich stream of observational data from each individual explosion and match spectral and light-curve fingerprints to recognize those that had the same peak brightness.

Within a few years of their classification, type Ia supernovae began to bear out that expectation. First, David Branch and coworkers at the University of Oklahoma showed that the few type Ia outliers–those with peak brightness significantly different from the norm–could generally be identified and screened out.4Either their spectra or their “colors” (the ratios of intensity seen through two broadband filters) deviated from the templates. The anomalously fainter supernovae were typically redder or found in highly inclined spiral galaxies (or both). Many of these were presumably dimmed by dust, which absorbs more blue light than red.

Figure 1 Light curves of nearby, low-redshift type Ia supernovae measured by Mario Hamuy and coworkers.7 (a) Absolute magnitude, an inverse logarithmic measure of intrinsic brightness, is plotted against time (in the star's rest frame) before and after peak brightness. The great majority (not all of them shown) fall neatly onto the yellow band. The Figure emphasizes the relatively rare outliers whose peak brightness or duration differs noticeably from the norm. The nesting of the light curves suggests that one can deduce the intrinsic brightness of an outlier from its time scale. The brightest supernovae wax and wane more slowly than the faintest. (b) Simply by stretching the time scales of individual light curves to fit the norm, and then scaling the brightness by an amount determined by the required time stretch, one gets all the type Ia light curves to match.5,8

Soon after Branch’s work, Mark Phillips at the Cerro Tololo Interamerican Observatory in Chile showed that the type Ia brightness outliers also deviated from the template light curve–and in a very predictable way.5 The supernovae that faded faster than the norm were fainter at their peak, and the slower ones were brighter (see Figure 1). In fact, one could use the light curve’s time scale to predict peak brightness and thus slightly recalibrate each supernova. But the great majority of type Ia supernovae, as Branch’s group showed, passed the screening tests and were, in fact, excellent standard candles that needed no such recalibration.6

Cosmological distances

When the veteran Swiss researcher Gustav Tammann and his student Bruno Leibundgut first reported the amazing uniformity of type Ia supernovae, there was immediate interest in trying to use them to determine the Hubble constant, H0, which measures the present expansion rate of the cosmos…….. Read the rest of this entry »

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October 4, 2011 at 3:21 pm

Nobel Prize in Physics 2011

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From left to right, Adam Riess, Brian Schmidt and Saul Perlmutter, who have won the 2011 Nobel Prize in Physics

The Nobel Prize in Physics 2011 has been awarded to Saul Perlmutter, Brian P Schmidt and Adam G Riess for discovering the accelerating expansion of the universe

Three scientists shared the 2011 Nobel Prize for physics for the stunning discovery that the expansion of the universe is speeding up, meaning it may one day turn to ice, the prize committee said on Tuesday.

Scientists have known since the 1920s that the universe is expanding, as a result of the Big Bang some 14 billion years ago, but the discovery that this process is accelerating — and not slowing as many thought — rocked the research community.

“If the expansion will continue to speed up, the universe will end in ice,” the Nobel committee said in a statement.

Half of the 10 million Swedish crown ($1.5 million) prize money went to American Saul Perlmutter and the rest to two members of a second team which conducted similar work — U.S.-born Brian Schmidt, who is based in Australia, and American Adam Riess.

“We ended up telling the world we have this crazy result, the universe is speeding up,” Schmidt told a news conference by telephone after the award was announced in Stockholm.

“It seemed too crazy to be right and I think we were a little scared,” he added.

Nobel Committee for Physics at the Royal Swedish Academy of Sciences said in its statement that the discovery was made by looking at distant, exploding stars.

Instead of their light becoming brighter, it was fading.

“The surprising conclusion was that the expansion of the universe is not slowing down. Quite to the contrary, it is accelerating,” the committee said.

The acceleration is thought to be driven by dark energy, although cosmologists have little idea what that is.

They estimate that dark energy — a kind of inverse gravity, repelling matter that comes close to it — accounts for around three quarters of the universe. –

Yes…‘s prediction is wrong again!! (anyway… read the commnent below…)

2011 Nobel Prize in Physics will be announced within the hour! Watch the live webcast here

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October 4, 2011 at 10:02 am

More Evidence For A Preferred Direction in Spacetime

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The evidence is growing that some parts of the Universe are more special than others

The dots on the unit sphere colored according to the sign and magnitude of the anisotropy level are the directions of the random axes. The hemisphere shown on the left panel is the one corresponding to larger accelerations with a preferred axis, while the right corresponds to the one with smaller accelerations and another preferred axis

One of the cornerstones of modern astrophysics is the cosmological principle. This is the idea that observers on Earth have no privileged view of the Universe and that the laws of physics must be the same everywhere.
Many observations back up this idea. For example, the Universe looks more or less the same in every direction, having the same distribution of galaxies everywhere we look.
In recent years, however, some cosmologists have begun to suspect that the principle may be wrong. They point to evidence from the study of Type 1 supernovas, which appear to be accelerating away from us, indicating the Universe is not just expanding but accelerating away from us. The curious thing is that this acceleration is not uniform in all directions. Instead, the universe seems to be expanding faster in some directions than others.
But how good is this evidence? Is it possible that the preferred direction is a statistical mirage that will disappear with the right kind of data analysis
Rong-Gen Cai and Zhong-Liang Tuo at the Key Laboratory of Frontiers in Theoretical Physics at the Chinese Academy of Sciences in Beijing have re-examined the data from 557 supernovas throughout the Universe and recrunched the numbers.
Today, they confirm that the preferred axis is real. According to their calculations, the direction of greatest acceleration is in the constellation of Vulpecula in the Northern hemisphere. That’s consistent with other analyses and also with other evidence such as other data showing a preferred axis in the cosmic microwave background.
That will force cosmologists to an uncomfortable conclusion: the cosmological principle must be wrong.
But it also raises exciting questions: why does the Universe have a preferred axis and how do should we account for it in our models of the cosmos?
Answers below!
Ref: Direction Dependence Of The Acceleration In Type Ia Supernovae

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September 7, 2011 at 2:14 pm

Molecules in supernova ejecta

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The fir rst molecules detected at infrared wavelengths in the ejecta of a Type II supernova, namely SN1987A, consisted of CO and SiO. Since then, con rmation of the formation of these two species in several other supernovae a few hundred days after explosion has been obtained. However, supernova environments appear to hamper the synthesis of large, complex species due to the lack of microscopically-mixed hydrogen deep in supernova cores. Because these environments also form carbon and silicate dust, it is of importance to understand the role played
by molecules in the depletion of elements and how chemical species get incorporated into dust grains. In the present paper, we review our current knowledge of the molecular component of
supernova ejecta, and present new trends and results on the synthesis of molecules in these harsh, explosive events….

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July 29, 2011 at 7:54 am

Supernovae, Neutrinos, and the Chirality of the Amino Acids

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Abstract: A mechanism for creating an enantioenrichment in the amino acids, the building blocks of the proteins, that involves global selection of one handedness by interactions between the amino acids and neutrinos from core-collapse supernovae is described.
The chiral selection involves the dependence of the interaction cross sections on the orientations of the spins of the neutrinos and the 14N nuclei in the amino acids, or in precursor molecules, which in turn couple to the molecular chirality. It also requires an asymmetric distribution of neutrinos emitted from the supernova.
The subsequent chemical evolution and galactic mixing would ultimately populate the Galaxy with the selected species.
The resulting amino acids could either be the source thereof on Earth, or could have triggered the chirality that was ultimately achieved for Earth’s proteinaceous amino acids (…..)

Part of the Veil Nebula (or NGC6960). The Veil Nebula is a faint remnant of a supernova that exploded some 5,000 years ago

If this model turns out to be correct, the longstanding question of how the organic molecules necessary to create and sustain life on Earth were created will have undergone a strong suggestion that the processes of the cosmos played a major role in establishing the molecules of life on Earth, either directly, or by providing the seeds that ultimately produced homochirality in the amino acids.
These molecules would appear to have been created in the molecular clouds of the galaxy, with their enantiomerism determined by supernovae, and subsequently either transported to Earth only in meteorites, swept up as the Earth passed through molecular clouds, or included in the mixture that formed Earth when the planets were created.
Any scenario in which these molecules were created exclusively on Earth in Darwin’s “warm little pond”, and supported by the experiment of Ref. [77], would find it much more difficult to explain the enantiomerism that is observed on Earth and, apparently, generally in the cosmos.
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June 25, 2011 at 7:48 am