Category: Astronomy

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Gamma-ray bursts (GRBs) are powerful blasts of energy that flash across the Universe. For a brief time, they are the brightest objects in the gamma-ray sky. Astronomers estimate that about 1,400 GRBs per year occur but because no one knows when and where they are going to appear, only a part of them happen to be detected. ESA’s Integral gamma-ray observatory detects about 10 GRBs a year, and those are of the big burst variety. But the spacecraft has observed several low-luminosity gamma-ray bursts, confirming the existence of an entire population of weaker bursts that have hardly been noticed so far. These aren’t just bursts from far away, but just weak bursts that are relatively close by. And astronomers are beginning to think these weak or faint variety of GRBs might be the most common.

When studying Integral’s gamma-ray burst data, Prof. Lorraine Hanlon from the School of Physics, University College Dublin, Ireland, and her colleagues, realized that some of the faintest bursts have distinctive gamma-ray emissions, and also present faint afterglows in the lower-energy X-ray and visible wavelengths.

Since, in general, GRBs are colossal explosions of energy triggered by the collision of very massive and compact objects such as neutron stars or black holes, or by the explosion of incredibly powerful supernovae, or hypernovae, one may think that these bursts are perceived as faint just because they take place very far away from us, in the remote corners of the Universe.

However, Prof. Hanlon and colleagues noticed that these faint bursts, just at the sensitivity threshold of IBIS, seem to originate in our cosmic neighborhood, within the nearby clusters of galaxies.

The study team suggests that the faint bursts may be generated by the collapse of a massive star that does not present the characteristics of a supernova, or by the merger of two white dwarfs (small and dense stars about the size of Earth), or by the merger of a white dwarf with a neutron star or a black hole.

“Past observations had already hinted the existence of faint GRBs, and thanks to Integral’s sensitivity we can now say that an entire population of them exist,” added Hanlon. “Actually, their rate may even be higher than that of the most luminous GRBs but, just because they are weaker, we may be only able to see those which are relatively close by.”

“More Integral observations in the coming years will definitively help us understand the phenomenon of faint GRBs, and to explore the nature of this newly observed population,” she concluded.

Source: ESA

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A few weeks ago, researchers announced the discovery of a “dark flow” of invisible matter tugging at distant galaxy clusters at the edge of the universe. Now comes more evidence of unseen and unknown forces in the cosmos, but this time its closer to home. A group of researchers have discovered that our particular part of the Universe — out to a distance of 400 million light years — is not expanding uniformly in all directions as expected. To be exact, the expansion is faster in one half of the sky than in the other. “It’s as if, in addition to the expansion, our ‘neighbourhood’ in the Universe has an extra kick in a certain direction,” says Mike Hudson from the University of Waterloo in Ontario, Canada. “We expected the expansion to become more uniform on increasingly larger scales, but that’s not what we found.” If confirmed, their findings will result in a new understanding of the origin of structure in the universe and possible revisions to the standard cosmological model.

Hudson and two other scientists have been conducting research on large-scale cosmic flows and the general expansion of the universe. This expansion increases the distances between galaxies steadily with time, and is called the Hubble flow. Deviations of the velocity of galaxies from the overall Hubble flow is called the “peculiar velocity.” By examining the peculiar velocities of clusters and superclusters scientists can obtain estimates of local mass concentrations that may be responsible for causing any deviations from the Hubble flow.

In particular, these researchers were attempting to address a longstanding question about the origin of the approximately 600 km/s peculiar velocity of the Local Group of galaxies, with respect to the Cosmic Microwave Background.

Using several different surveys they discovered that about 50% of the Local Group’s motion is faster than anticipated. To produce this motion, they believe there must be large unseen and unknown structures in the universe. They write, “The large value of the residual motion implies that there are significant velocities generated by very-large scale structures,” and the structures lie beyond the Local Group.

Brian McNamara, a University Research Chair in UW’s department of physics and astronomy, says Hudson is finding that much of the matter in the nearby universe moves as an ensemble with a surprisingly high speed. “If the work he and others are doing is confirmed, it will require a major revision in the way we think the universe came into being and how it evolved.”

Hudson and his colleagues have submitted a paper to the Royal Astronomical Society, and a preprint version is available here.

Sources: arXiv, University of Waterloo

Question: What is the far side of the Moon?

Answer: Did you ever notice that the Moon always looks the same? Sure, it waxes and wanes from a new moon to a full moon, but the bright and dark patches on the Moon always look the same. In fact, these features are so familiar that people call it the Man in the Moon.

This is because the Moon always points the same face towards the Earth. The Moon does actually rotate on its axis, it’s just that the amount of time it takes to make a complete orbit around the Earth matches the amount of time it takes to complete one rotation. In both cases, this is 27.3 days.

So, when you hear people refer to the far side of the Moon, they’re talking about the part of the Moon that always faces away from the Earth. Until we sent spacecraft into orbit around the Moon to take pictures, nobody on Earth had ever seen what the far side of the Moon looks like.

But why does this happen? Over the few billions years since its formation, the Moon has become tidally locked with the Earth. In the distant past, the Moon had different rotation and orbital speeds, and it showed all of its sides to our planet. But the gravity of the Earth tugged at the irregular shapes on the Moon, causing it to slow its rotation down until it was exactly the same length as its orbit.

The Earth, on the other hand, has so much mass that the force of gravity from the Moon pulling on Earth can’t overcome its rotational speed. The Moon does create the tides, though, and causes the ground to rise and fall – it’s just such a small amount that you can’t feel it.

Sometimes people mistakenly call this the dark side of the Moon. But there is no dark side of the Moon. Think about it, when we’re seeing a new moon, that’s because the familiar part that we can always see is in shadow. But at that point, the far side will be bathed in sunlight.

Hopefully you’ve heard about the International Year of Astronomy — a year long celebration in 2009 of the 400th anniversary of Galileo’s first look through the telescope. One part of that celebration is the 365 Days of Astronomy Podcast. There will be one podcast per day, every day, for all 365 days of 2009. The podcasts will be 5 to 10 minutes in duration, and will be available through the 365 Days of Astronomy website and an RSS feed. The 365 Days team has just put out a trailer encouraging everyone to listen every day:

Want to be part of the project?

Not only will you have the chance to listen each day, but you can participate as well. The podcast episodes will be written, recorded and produced by people around the world. Each day will have a specific topic or theme based on The 365 Days of Astronomy Calendar, a daily calendar of astronomical events, themes and ideas created by the IYA.

People participating can choose their own topics, all of which will need to be approved ahead of time. For all the details head on over to the website. And if you’ve never recorded anything before, never fear. There’s even information on how to record a podcast, as well as much more.

You can also follow 365 Days of Astronomy on Twitter.

And, if you thought you’ve heard the voice on the video before, its none other than the golden voice of Mat Kaplan from Planetary Radio.

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We don’t normally publish political articles here on Universe Today, but I’m going to make an exception here after watching last night’s presidential debate because a.) John McCain mentioned something about a planetarium, which is an area of interest for UT readers, and b.) McCain obviously had no idea what he was talking about. McCain, the Republican presidential nominee pointed out how Barack Obama, the Democratic nominee, has voted for almost a billion dollars of “pork barrel” projects (money for specific pet projects in their districts) and said, “He (Obama) voted for … $3 million for an overhead projector at a planetarium in Chicago, Illinois.”

First of all, there’s a big difference between an overhead projector and a planetarium projection system. Spacewriter’s Ramblings has a great explanation and pictorial description, if you have questions.

Second, if you want to be nitpicky, while Obama requested the funding, he never voted on it.

Obviously, McCain thinks this is a big issue, since this is at least the second time he’s mentioned Obama and planetariums. A few weeks ago he said that Obama has sought money for “planetariums and other foolishness.”

Foolishness! Over 110 million people around the world visit planetariums every year! They are important learning and teaching tools that encourage a science-literate population, and have inspired young people to become astronomers and astronauts, and aspire to many other science-related occupations as well.

Davin Flateau says it much better than I can on his great post at his Perfect Silence blog.

Obama’s website has a list of his federal funding requests for Fiscal Year 2008, and clearly listed is “Adler Planetarium, to support replacement of its projector and related equipment, $3,000,000,” with a description that says the 40 year old projection equipment has begun to fail and since parts are no longer available, soon students and other museum-goers will be left “without this very valuable and exciting learning experience.” I don’t see that as “pork barrel” funding, but an attempt to maintain a long-standing (Adler opened in 1930) and important institution in his district.

And don’t get me going on Sarah Palin.