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Coincidentally, about those exploding stars. . .

October 24, 2011 Leave a comment

An exploding star can release a massive amount of energy, an event called a gamma ray burst, as shown in this National Science Foundation illustration. But it's hard sometimes to tell the different between a statistical blip in data from the real thing.

An exploding star can release a massive amount of energy, an event called a gamma ray burst, as shown in this National Science Foundation illustration. But it's hard sometimes to tell the difference between a statistical blip in data from the real thing.


Phil Evans, an X-ray astronomer in England and frequent guest blogger for Geeked On Goddard, sends us this report on the fascinating nature of coincidence in science.


I have the power to make stars explode!

No, seriously. True, I can’t draw my sword and turn miraculously into a muscle-bound hero, like He-Man, nor can I turn my pet cat (Tinkabell) into Battle Cat, He-Man’s ferocious feline familiar.

But I really can make explosions at the other end of the universe. Skeptical? Here is the proof:

Last year, NASA’s Swift satellite (data from which I use in my work) was going through a bit of a lean observing period, with no gamma ray bursts (GRBs) detected for some time. GRBs are vast releases of energy from collapsing or collidign stars.

So, just as my duty week began at the University of Leicester, I tweeted, “Wake up universe!”

In the next 24 hours, Swift snagged four GRBs. Coincidence?

The only other time that we have had that many bursts in one day was the day celebrated science fiction author Arthur C. Clarke died? Coincidence?

Well, actually — yes. The thing is that coincidences happen all of the time.

A couple of years ago on her BBC Radio show, Sarah Kennedy asked people to send in their “coincidence” stories. Countless people mailed in about times they’d gone around the world on holiday, and met someone from three streets away. The response was continually, “Wow! Isn’t that amazing?” when what the was program actually demonstrating was that these “unlikely” events actually happen regularly.

In fact, when people respond to these stories by saying, “Small world,” they’ve got it totally wrong! It’s because it’s a big world that these things happen. Imagine something that only affects 1 in a million people. Pretty unlikely? Well, it will affect something like 300 Americans, and 60 Brits!

image of possible gamma ray burst

Image of possible gamma ray burst, or statistical blip? (click to make me big)

Coincidences happen. And this can be a real pain for astronomers. I’ve got some data, there’s a cluster of pixels close together. Is it a faint source, or just a coincidence that some background light has clustered? (See image at right.) This spectrum shows a blip. Is it a real feature, or just noise?

Fortunately, using statistics we can at least quantify how likely things are. Typically in astronomy we would only claim we’d found a source, for example, if there was less than a 0.3% chance that it was just a “lucky” fluctuation in the background. Even this happens, well, 0.3% of the time!

For Swift, we have to be even more conservative. When the Burst Alert Telescope (BAT) thinks it’s found a GRB, there has to be only a 0.0000000000008% chance that it’s just a fluctuation in the background [for us to interpret the observation as “probably real.” This threshold was carefully determined to minimize the number of false alarms, without losing real (possible) GRBs.]

Despite this, we do get a few false alarms every year, because of the number of times and ways the BAT looks for GRBs. We tried a “subthreshold” test a couple of years ago, where we triggered on things which were more likely to be spurious, that is, there was a 0.00000000006% chance of them being a random change in the background. We expected, and got, about 2 false alarms a day.

Overall, I’d say we get maybe 5 false alarms a year — but about 100 real GRBs. And the false alarms we usually identify within 20 minutes or so, so they take very little of our time.

So, next time someone tells you something unusual that’s happened, and asks if it could be coincidence, the best answer is probably, “Yes!”

Check out Phil’s twitter feed: @swift_phil

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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The latest findings on the star-eating black hole

swift star eater


Phil Evans, an X-ray astronomer in England and frequent guest blogger for Geeked On Goddard, sends us this report on some exciting new findings of the NASA Swift observatory.

Back in March this year the Swift satellite detected a massive explosion in space. That in itself is nothing new. Indeed, it’s what Swift was designed to do. But, as I posted back in April, this one was a bit strange. Whereas Gamma Ray Bursts — Swift’s bread-and-butter (how cool, by the way, to be describing the most powerful explosions known in such an off-hand way) — explode and then fade away, this object flared up again, and again and then a fourth time, and even now is a bright source of X-rays.

So what was it? As I noted in that post, just 3 weeks after the event, a consensus has already formed that this was an extremely rare event: a star being torn apart by a black hole. Two papers have today (August 25) been published in the journal Nature, arguing for this interpretation, one of them led by Prof. David Burrows — the head of the X-ray Telescope (XRT) team on the Swift satellite. Here is a University of Leicester press release on the discovery.

The aftermath of such an event has been seen before (occasionally), but only well after the event, where all that can be seen are the last dregs of material being gobbled up: the black hole licking its lips, if you like. With Swift, for the first time, we’ve now seen the process actually starting, the black hole taking its first bite.

And, in doing so, we found something new: the light we saw can’t be explained by the standard models of a star being torn apart by a black hole. Incidentally, the black hole was a few million times more massive than the Sun!

Instead, the process must have resulted in the light coming out along a narrow ‘jet’ of material. Keen followers of Swift will notice that this is also how Gamma Ray Bursts emit their light.

Setting GRBs aside, jets from black holes at the center of a galaxy are a very common phenomenon, seen in Active Galactic Nucleii for example, but we’ve never seen such a jet actually ‘turn on’, until now. This once again highlights how awesome it is to working on Swift. At any moment I could be interrupted by an SMS from the spacecraft. Maybe it will be ‘only’ a huge explosion from the other side of the universe. Or maybe it will be something completely new.

Follow Phil Evans on twitter: @swift_phil


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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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Swift Detects Most Distant Object In The Universe! AGAIN!

May 25, 2011 2 comments

Now where have we heard THAT news before? For aficionados of NASA’s Swift satellite, or even space science and astronomy in general, this headline probably rings a few bells. Like this one for example, announced on April 28, 2009:

New Gamma-Ray Burst Smashes Cosmic Distance Record

But what many of you may not be aware of is that, within 24 hours of the April 28 headline, Swift detected yet another gamma-ray burst (the death-throes of a massive star), which was even more distant. Why didn’t you know? Well, because we didn’t either!

image of GRB 090429b
A Gemini Observatory color image of the afterglow of GRB 090429B, a candidate for the most distant object in the universe. This “izH” image has been constructed from three images taken at the Gemini Observatory North telescope through different optical and infrared filters. The red color results from the absence of all optical light, which has been absorbed by hydrogen gas in the distant universe. Without that absorption, the afterglow color would be bluer than any of the galaxies and stars seen here. (Credit: Credit: Gemini Observatory/AURA/NASA/ Levan, Tanvir, Cucchiara, Fox)

The explosion, termed GRB 090429B, was detected on April 29, 2009, by Swift. Nino Cucchiara and his then-PhD supervisor Derek Fox, along with collaborators including Nial Tanvir and Andrew Levan from the UK, observed the GRB with the 8-meter Gemini telescope in Hawai’i, and found that it was red. Very red.

Now this can mean two things: either it’s a really long way away, or it went off in a really dusty galaxy. So Nino and collaborators asked the Gemini operators to take a spectrum of the source, which would provide a measurement of the object’s distance.

Unfortunately, even on Hawai’i, astronomers are at the mercy of the weather. And just as Gemini prepared to take the spectrum, the weather turned and observing was impossible. By the next observing opportunity, the GRB was too faint to take a usable spectrum.

Fortunately, that’s not the end of the story, but it made the job much harder. Now, after two years of hard graft, and observations with Gemini and with the Hubble Space Telescope, Nino and collaborators have released their findings. And the cosmic record holder has fallen!

Well, probably. Their result shows, based on analysis of the images, that there is a 99.3 percent likelihood that this object was more distant that GRB 090423 — the object being trumpeted just before this star exploded. The precise distance is not known because of the lack of spectrum, but there is a 98.9 percent chance that is lies further away than a galaxy discovered in 2010 — 13.07 billion light years away — which surpassed April 2009’s GRB 090423 as the most distant known object. Whether it is the farthest object ever seen is not entirely clear: a galaxy detected in 2011 may lie a little further away…. or may actually not be a distant object at all.

Either way, this new result is another triumph for GRB science, for Swift and the optical and infrared facilities like Gemini, and above all for the hard-working determination of the scientists studying these enigmatic phenomena.

Follow Phil Evans on twitter: @swift_phil

Has-been: In 2008, GRB 080319b had it's 15 minutes of fame as the farthest known object in the universe.

A gamma-ray burst is a tremendous release of energy triggered by the collapse of a massive star.

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.


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Phil Evans' Swift Universe: It's official — NASA's Swift satellite reveals a galaxy eating a star!

April 20, 2011 1 comment

Here is another guest post from Swift X-ray astronomer Phil Evans, “our man in the Midlands.” This time it’s an update about the galaxy that ate a star. — gogblog


Hungry? Fancy a snack? How about eating a star?

That, it seems, is what happened at lunchtime (in the UK) on March 28th. Here is an image of the burst from the Swift X-ray Telescope:


swift_grb_image_600

The Swift satellite detected what was at first thought to be a long Gamma Ray Burst (GRB), much like the 90-odd we detect every year although a bit on the long side. But then it “went off” again.

GRBs don’t do that. As it happens, I had just left to play football (alright, soccer if you insist) so I missed this second outburst, and I should point out that, although as your friendly blogger I’m telling this tale, it’s not my tale and I can’t claim any of the credit (alas!).

In fact, the first indication to me that this was a special event came that evening when, as I was replacing the grease filter in my cooker, my mobile phone rang. After degreasing myself enough to answer it I found that Dave Burrows, head of the Swift X-ray telescope team, asking if I could double-check some of the automatic results my code produces, because this object appeared to be weird.

(By the way, my twitter followers @swift_phil were among the first to learn that Swift had found something exciting and new!)

Weird it was. Gamma Ray Bursts get fainter over time. This didn’t, and hasn’t. Swift triggered on outbursts from it 4 times in 48 hours, and in the X-rays it remains bright today. (Back on April 7, NASA issued a press release about the event by science writer Francis Reddy.)

So what is it? Many astronomers have trained their telescopes on it in the past few weeks, taking data and reporting it quickly. Andrew Levan from Warwick University (UK) and collaborators used the Gemini telescope and found that the object was about 5 billion light years away! Further observations with infra-red and radio telescopes showed it to be right at the centre of it’s host galaxy.

Although only three weeks have passed since the event, papers are already appearing online. The consensus which is forming suggests that what Swift saw was a star straying too close to the super-massive black hole at the centre of its galaxy. The unfortunate star was torn apart and the pieces are now being gobbled up by the hungry black hole!

We’ve seen evidence for these events before — after the event — but Swift has captured yet another first: actually catching the black-hole perpetrating its massacre red-handed!

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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Phil Evans' Swift Universe: Contemplating the inconstancy of the Crab

January 12, 2011 Leave a comment

New results from NASA space observatories have revealed something surprising about the Crab Nebula: This famous supernova remnant — long considered a veritable “old faithful” of X-ray sources for the constancy of it energy output — appears to be dimming over time. We asked Phil Evans, gogblog’s on-call X-ray scientist and a member of the NASA Swift Observatory science team, to tell us why the inconstancy of the Crab is so important to astronomers.

image of crab nebulaThe Crab Nebula has a prestigious history. It formed when a star exploded in a supernova, and was first observed and recorded by Chinese observers in 1054 AD. The glow of the supernova was so bright, people could see it during the day for more than 3 weeks!

The material which was blown off the star has been expanding since then in a complex structure with leg-like filaments that earned it its name. It’s also a very bright source of X-rays, and — particularly usefully — its brightness and spectrum don’t change; so astronomers can (and do) use it to calibrate their X-ray instruments. In fact, “a Crab” is an internationally recognized unit of measurement.

The problem is, these new results suggest that the Crab is not constant after all, according to a press release issued today by NASA’s Goddard Space Flight Center. The measurements taken over the last few years by the Fermi, Swift, RXTE and INTEGRAL satellites show that the Crab actually varies by a few percent every year. This is not too disastrous right now: It’s pretty hard to calibrate high-energy instruments to an accuracy of 1 percent or so, and the definition of “a Crab” as a unit of measurement has a fixed definition. But as technology advances, we will probably find that the Crab is no longer the ideal calibration source.

This type of finding, by the way, is not unusual. It is often the case that an object described as the “protoype” of its class turns out to be atypical! Indeed the star Vega, long used as a standard in optical astronomy, was recently found not to be standard. The exciting thing about all of this is it shows us how much we still have to learn. The Crab is among the brightest X-ray sources in the sky, and yet it is able to jump out and surprise us.

In a related point under the same press release, recently published work from the NASA’s Fermi Gamma-ray Space Telescope and the Italian Space Agency’s AGILE satellite have found large gamma-ray flares from the Crab Nebula. Investigation is ongoing, but this may indicate a really strong electric field. As study coauthor Stefan Funk said, “The strength of the gamma-ray flares shows us they were emitted by the highest-energy particles we can associate with any discrete astrophysical object,” which in themselves present plenty of challenges.

The Crab nebula: exciting and enigmatic? Yes! Constant and well understood? No! A fantastic natural laboratory? You bet.

— Phil Evans

Follow Phil on Twitter to get updates on his life and work in X-ray astronomy.
@Swift_Phil

chart of declining crab nebula x-ray output

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.


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Time-lapse photography of the partial solar eclipse this morning, photographed from England

January 4, 2011 1 comment




Phil Evans, an X-ray astronomer in England and frequent guest blogger for Geeked On Goddard, sends us this report on the partial solar eclipse this morning. The video above consists of 50 still shots taken by Phil over a 15-minute period. The music is Mars, Bringer of War, by Gustav Holst, brought to you in its copyright-free glory by the U.S. Air Force Band.

Being a Brit and an astronomer is often no fun. The clouds know when something interesting is happening, or you’ve bought a new piece of equipment. Almost every lunar eclipse I’ve tried to watch has been clear until the moon was about 30% covered, and then I was clouded out until the moon was about 30% covered on the way out of eclipse.

So it was with extreme pessimism that I began my first working day of 2011 by trudging my way up to the 5th floor of a tall campus buiding, carrying my brand-new Canon EOS 500D (a Christmas present plus my savings!). Sure enough, as the sky began to glow, two large, banks of cloud were illuminated near the horizon. Typical!

Or not.

Actually, there were two small, sun-size gaps: one between the horizon and the first bank, and one between the two banks. As the Sun rose (surprisingly quickly) we were treated to a fantastic view of the crescent Sun above the trees, distorted by the atmosphere, and actually accentuated by the clouds. They added depth, colour and an extra sense of anticipation as the Sun, rather than baring all, made use of the available cover to dance suggestively, keeping us on the edge of our seats.

108 photos later and the cloud had taken over. But was it worth the climb up 5 floors at 8 a.m.? You bet it was. Nice one, Universe.

— Phil Evans

Follow Phil on Twitter to get updates on hius life and work in X-ray astronomy.
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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.


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Phil Evans Swift Universe: how nature's strongest magnets power some of nature's brightest blasts

November 4, 2010 Leave a comment

A magnetar formed inside a collapsing massive star

A magnetar formed inside a collapsing massive star

Today “Swift Universe” guest blogger Phil Evans brings us some breaking news from the Gamma Ray Bursts 2010 conference in Annapolis, Maryland.

You’re all familiar with magnets. Well, two of my colleagues at the University of Leicester — Professor Paul O’Brien and his graduate students Antonia Rowlinson and Nicola Lyons — have announced evidence that some gamma-ray bursts (GRBs) are powered by stars called magnetars — super-strong magnets in space, if you like.

The idea is that, when the GRB goes off, the core of the dying star may not collapse straight to a black hole but instead could live for a couple of minutes as a rapidly rotating, magnetic neutron star called a magnetar. The magnetic field acts like a brake slowing the magnetar down and pumping its energy into the GRB, until after a few minutes the star has slowed down and collapses into a black hole.

Using data from the Swift satellite, my colleagues found that some GRBs show a period of constant brightness and then suddenly get really faint: just as the magnetar model predicts.

“So what?” you may ask. Well, GRBs are pretty much unique tools to study the early universe, and it’s the deaths of massive stars, some of which die as GRBs, which gives the universe the chemicals that you are I are made from. Getting a handle on the processes by which a star dies, and how it gives off its energy, is fundamental to using GRBs to study these matters. Showing that some GRBs are powered by magnetars is a big step forward.

One note of caution though: this isn’t “the” answer. While it seems to be the only explanation for some GRBS, in this same conference scientists from Berkeley university have shown using data from the Fermi satellite that the brightest GRBs can’t be powered by magnetars, but need a black hole right from the word go. Life’s never straightforward… but it’s often interesting!

Follow Phil as a Swift scientist on Twitter:  @Swift_Phil

Ron Cowen at Science News published a detailed write-up on the research.

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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Phil Evans' Swift Universe #1: a blinding X-ray GRB, the "nonsense and half-truths" of the science news cycle, and the thrill of prising open Nature's secrets

September 1, 2010 Leave a comment

*** gogblog is happy to announce a new guest blogger: Phil Evans. He’s an X-ray astronomer in England who taps into NASA’s Swift satellite for data. Swift is managed, as a project, from Goddard Space Flight Center, but it was developed by scientists in the United States, the United Kingdom, and Italy. Phil works at the University of Leicester in England’s East Midlands.

In an earlier post, I told the story of how Phil discovered a blindingly bright (in X-rays) gamma-ray burst. In “Swift Universe,” Phil will give us a backstage peek at the life of an X-ray astronomer and Swiftophile. Here’s his first post, where he gives you the low-down on Swift and his role in the mission.

Flash! X-rayss from this collapsing star temporarily dazzled NASA's Swift satellite

Flash! X-rays from this collapsing star temporarily dazzled NASA's Swift satellite

Welcome to the first Swift Universe blog, where you’ll get a (hopefully) insightful and (if you’re lucky) entertaining update on what’s going on in the universe, at least as far a member of the Swift satellite team is concerned.

Swift is a satellite which was launched in 2004 to study gamma ray bursts. These are thought to be the most powerful explosions in the universe. A typical gamma-ray burst, or GRB, gives off in 10 seconds as much energy as you would need to run your microwave for around 400,000,000,000,000,000,000,000,000,000,000,000 years, which is 30 million million million million times the age of the universe. Don’t try it; the bill will be horrendous.

I work in the UK branch of the Swift team, at the University of Leicester. I am part of the XRT team (that’s the X-Ray Telescope on Swift) and also part of the UK Swift Science Data Centre. My day to day work involves looking at the X-ray data from Swift and producing web-based tools to help scientists use these data.

Just recently I was involved in one of Swift’s discoveries: finding the brightest X-ray flash from outside our own galaxy ever seen. Not only was it exciting as a scientist, but it proved to be a very educational experience for me, as I was for the first time involved in writing a press release.

Although I’ve been tweeting in my role as a Swift scientist for some months now, I’ve never had to write more than 168 characters announcing something work-related to the public, and it was quite surprising how tough it was. All my natural instincts were to start blabbering on about pile-up, exclusion regions, correction factors, and ergs per second — most of which probably means nothing to most people.

Fortunately, press officers at NASA and Penn State University — and your own Geeked on Goddard blogger — were on hand, and they knew (as I now do) that “this was so bright it dazzled our telescope” conveys the “wow” factor much better than just floating numbers around does! It was a very good experience for me, and a reminder of how important it is for scientist to learn to communicate with the public. (See the Penn State press release about the X-ray GRB.)

click me to see the cartoon!

click to see the cartoon!

I am reminded of an excellent PhD Comic item lampooning “The Science News Cycle.” The jokes are a bit of an exaggeration, but not always so far from the truth!

And I think in the age of the Internet, where nonsense and half-truths can spread so quickly, it’s increasingly important for scientists to communicate properly. Take all of the climate change skepticism that exists at the moment for example. Why is it that so many people who are not trained scientists and without having conducted extensive research, tend not believe the scientists who really are experts?


“. . . in the age of the Internet, where nonsense and half-truths can spread so quickly, it’s increasingly important for scientists to communicate properly.”


I don’t know the answer, but if scientists were as good at communicating their research as skeptics and conspiracy theorists are at communicating their doubts, perhaps this situation would not exist.

Like a lot of us, you might be wondering WHY that GRB was so bright in X-rays, especially as it was at other wavelengths a fairly typical burst. Right now, we still don’t know.

I suppose you could call this the “unsexy” part of the science, although this can be where the real excitement comes and you just can’t see it. In public we show the thrill of the discovery, and eventually the satisfaction of writing a paper explaining it. (This effort will be led by Tilan Ukwatta at Goddard Space Flight Center, who was the duty scientist with overall responsibility for this GRB).

But in between comes the real work and (for us) the real fun. It’s the subtle cut and thrust duel with the universe as we try to prise open its secrets, exploiting the details of our data, battling with their limits and finding out how it all fits into the bigger picture. It probably doesn’t make for exciting reading as we go along (“Within 3-sigma we’re consistent with the k=2 closures, assuming…..”) but when you consider the vastness of the universe, plugging away at its mysteries is a real privilege, and the reason we’re in this business.

My own current theory probably won’t make it into the scientific paper: this year the University of Leicester celebrates 50 years of performing space science research. Although the GRB went off before the celebratory conference, thanks to my holiday we didn’t make this discovery until the conference has started. So the cause is obvious: the universe was saying “Happy Birthday” to Space Science at the University of Leicester!

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OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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