Category: Astronomy

The Swift satellite has made another fortuitous observation. This time, and for the first time ever, astronomers have caught a star in the act of going supernova. These stellar explosions have been observed before, but always after the fireworks were well underway. “For years we have dreamed of seeing a star just as it was exploding, but actually finding one is a once-in-a-lifetime event,” says Alicia Soderberg, from Princeton University, who is leading the international group studying this explosion. “This newly born supernova is going to be the Rosetta Stone of supernova studies for years to come.”

In January of 2008 Soderberg was expecting to study a month-old supernova that was already underway. But as she and her assistant studied the X-ray emissions conveyed from space by NASA’s Swift satellite, they saw an extremely bright light that seemed to jump out of the sky. They didn’t know it at the time, but they had just become the first astronomers to have caught a star in the act of exploding.

“In the old days — last year — people found supernovae by their optical light and then started to study them to understand which stars blow up, what the mechanism is and what they produce,” said Robert Kirshner, a professor of astronomy at Harvard University. “But this is something new — the X-rays come right at the beginning and provide a very early alert to the event.”

Soderberg regards the discovery as a case of extreme serendipity. The satellite was pointing in the right place at the right time, she said, because she had asked Neil Gehrels, Swift’s lead scientist at NASA’s Goddard Space Flight Center to turn it that way to look at another supernova. And while she was away lecturing, she had asked her colleague, Edo Berger, to keep an eye on the data for her.

“It’s a really lucky chain of events — a surprise,” said Soderberg, who is leading the group studying the explosion. “It was all over in a matter of minutes.”

Other observatories also turned their telescopes toward this stellar explosion, making detailed observations of the event, including the Hubble Space Telescope, the Chandra X-ray Observatory, Palomar’s 60- and 200-nch telescopes, the Gemini Observatory and Kitt 1 Telescope in Hawaii, and the Very Large Array and Apache Point Observatories in New Mexico. This will allow a very detailed study of this event.

A typical supernova occurs when the core of a massive star runs out of nuclear fuel and collapses under its own gravity to form an ultradense object known as a neutron star. The newborn neutron star compresses and then rebounds, triggering a shock wave that plows through the star’s gaseous outer layers and blows the star to smithereens. Until now, astronomers have only been able to observe supernovae brightening days or weeks after the event, when the expanding shell of debris is energized by the decay of radioactive elements forged in the explosion.

Original News Source: Princeton University Press release

The life of NASA’s Compton Gamma Ray Observatory (CGRO) ended in 2000 when the spacecraft’s remains splashed down in the Pacific Ocean after a planned deorbit. But the space telescope’s spare parts live on, and they may have a new job. Instead of searching the universe for radioactive emissions, they could help military personnel search for dirty bombs and other radioactive materials. “If we can detect radioactive aluminum-26 on the other side of the galaxy we can find other radioactive materials like cesium-137 or cobalt-60 inside a building or on the other side of the street by the same method,” said Dr. James Ryan from the University of New Hampshire.

Ryan was a member of the research team that helped build and operate the gamma-ray imaging COMPTEL telescope onboard the CRGO, a 1991-2000 NASA mission. One of the key findings of COMPTEL was its map of radioactive aluminum from dying stars throughout the Galaxy.

Identical flight spares of all the telescope components were built, just in case any of the parts failed. While the spares were never launched, they haven’t been collecting dust on a shelf. At different times, Ryan told Universe Today, the flight spares were assembled into a working telescope, sometimes as a student exercise and once for the benefit of the US Army as a test for probing the interior of buildings based on the background gamma radiation being emitted from the contents of the building.

“It is a sensitive instrument and it required no great thought to envision this use for it,” Ryan said of his idea to use the parts to pinpoint the location of dirty bombs. He was motivated by witnessing a National Guard drill to search for and clean up radioactive material left over by “terrorists.”

“It was clear that we would be able to sense the presence and approximate location of the radioactive material without entering the building with this device,” he said.

The device, known as GRETA, short for the Gamma-ray Experimental Telescope Assembly, could potentially be loaded on a truck and used for homeland security work such as scanning shipping containers or buildings for radioactive materials.

GRETA can accurately determine the direction from which a radioactive source is being emitted by creating an image, unlike current technology used by the military, such as Geiger counters or spectrometers that can only determine that radiation in is the vicinity.

“They might detect the presence of cesium-137 but they won’t know where it is unless they get right up close to it, they would have to fish around inside the building,” said Ryan, which would be a safety issue for military personnel.

Other media outlets report that some scientists doubt the applicability of this technology, saying GRETA’s “older” design has its limitations. But Ryan told Universe Today that current technology has changed very little from what COMPTEL, and GRETA, employ.

“Few, if any, scintillator detectors today will perform better than what is in GRETA,” he said. “There are newer designs for gamma-ray telescopes under development, but they are far from a deployable state. All are expensive, far more than a GRETA-type instrument. In fact, one could argue that GRETA is optimized for this application, because it provides the sensitivity necessary for the imaging and spectroscopy, while still remaining affordable and deployable on a short time scale.”

While GRETA is a prototype, the blueprints for the detectors, electronics and operation software still exist and can be used, with little modification, to build up a commercial unit for a real field test.

Ryan said there could be several potential “customers” or users for this device. “The National Guard is an obvious one, because they are charged with the clean up and disposal problem if, and when, a terrorist cell is uprooted. The US Border Patrol, various branches of the military and different port authorities could all find this useful,” Ryan said.

More information about CGRO.

The whole point of putting telescopes in orbit is to avoid distortions caused by our murky atmosphere. But now astronomers say they have calculated only half the light of our universe reaches telescopes, even those in orbit, because of the amount of dust that permeates the universe. In essence, they say, the universe is twice as bright as previously thought. The lead author of a new paper detailing this discovery, Dr. Simon Driver from the University of St Andrews said, “For nearly two decades we’ve argued about whether the light that we see from distant galaxies tells the whole story or not. It doesn’t; in fact only half the energy produced by stars actually reaches our telescopes directly, the rest is blocked by dust grains.”

While astronomers knew the universe contains small grains of dust, they hadn’t realized the extent to which this is restricting the amount of light that we can see. The dust absorbs starlight and re-emits it, making it glow. They knew that existing models were flawed, because the energy output from glowing dust appeared to be greater than the total energy produced by the stars.

Dr. Driver said, “You can’t get more energy out than you put in so we knew something was very wrong. Even so, the scale of the dust problem has come as a shock – it appears that galaxies generate twice as much starlight as previously thought.”

The team used a new model of the dust distribution in galaxies from a catalogue of 10,000 galaxies to precisely calculate the fraction of starlight blocked by the dust. The team says dust blocks approximately half of the light that the Universe generates.

The Universe is currently generating energy, via nuclear fusion in the cores of stars, at a whopping rate of 5 quadrillion Watts per cubic light year, about 300 times the average energy consumption of the Earth’ population.

After measuring the brightness of thousands of disc-shaped galaxies with different orientations, the astronomers matched their observations to computer models of dusty galaxies. From this they were able to calibrate the models and, for the first time, determine how much light is obscured when a galaxy has a face-on orientation. This then allowed them to determine the absolute fraction of light that escapes in each direction from a galaxy.

While modern instruments allow astronomers to see further into space, they can’t eliminate the obscuring effect from these tiny dust grains. “It is somewhat poetic that in order to discover the full glory of our Universe we first had to appreciate the very small” said Dr. Alister Graham from the Swinburne University of Technology.

The team consists of astronomers from the United Kingdom, Germany and Austrailia. Their research was published in the May 10 issue of Astrophysical Journal Letters.

Original News Source: Science and Technology Facilities Council

If you haven’t yet discovered Astronomy Picture of the Day, its an absolutely wonderful site that provides a different image every day of our universe, with explanations written by two professional astronomers, Robert Nemiroff and Jerry Bonnell. Today’s APOD post is not a picture, however, but a movie. Combining data taken from the Mars Reconnaissance Orbiter and the Mars Rover Spirit, Doug Ellison from UnmannedSpaceflight.com created a movie that simulates a fly-over of the Columbia Hills region on Mars. Of course, the Hills were named in memory of the astronauts who died in the Columbia space shuttle accident in February 2003.

In the movie you see the rippled sand on the sides of the Hills, the peak on Husband Hill where Spirit triumphantly climbed and surveyed the amazing view, and a white-colored area back on lower ground called Home Plate that Spirit has been studying for a couple of months now. Spirit herself makes a cameo in the video, too. It’s just great fun to watch.

Well, instead just reading about it, go visit APOD to watch the movie. And stay and browse awhile: APOD boasts the largest collection of annotated astronomical images on the internet.