National Aeronautics and Space Administration

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.



The 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

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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.



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.

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.

ABOVE: The X-ray nova MAXI J1409-619 before (October 12) and after (October 17) it dramatically brightened.


What’s new in cosmic X-rays? This is: Astronomers in Japan, using an X-ray detector on the International Space Station, and scientists at Penn State University, using NASA’s Swift space observatory, have just discovered a new X-ray nova hiding inside our Milky Way galaxy in the constellation Centaurus.

Ho, hum, another day, another X-ray nova. I’m not an expert in cosmic thingies that emit X-rays, but I know someone who is: Phil Evans, gogblog’s on-tap X-ray astronomer. He’s a post-doctoral research assistant in the X-ray and Observational Astronomy group at the University of Leicester, and has previously appeared on the blog. I asked him to explain why this discovery is interesting. You can also read the Penn State press release for lots of details.

Gogblog:  Ok, Phil, so what’s the big deal about this X-ray nova?

Phil Evans: This may be a new Supergiant Fast X-ray Transients, or SFXT. It’s a class of object which INTEGRAL discovered, through their outbursts — Swift has since shown — are actually not so fast or transient at all!

These systems contain a giant star and a compact object such as a neutron star or black hole. Their orbit is rather eccentric — more an oval than a circle. The outbursts here occur because the giant star has a strong wind, blowing its outer layers off. As the stars pass close to each other, the compact object slams into this wind and a shock front forms ahead of it, heating the material up so that it emits X-rays.

What Swift has shown for many of these sources is that actually they emit X-rays outside of outburst as well. For — most of, maybe all of — the rest of the orbit, where the compact object is not shocking the giant star’s wind, it’s actually sucking it up. This wind falls onto the compact object and as it slams into the surface of the compact object it gets heated up and also gives off X-rays, albeit at a much lower rate than in outburst.

Gogblog: Two teams observed this thing, right? First scientists in Japan, who then alerted the Swift observatory to follow up.

Phil Evans: Yes. And this is a great example of why international collaboration is so important. The sky is so big that to spot something like this — a sudden bright outburst in soft X-rays— is almost impossible unless you have some device which looks at a large part of the sky, something like the MAXI instrument, which sits on the ISS and scans the whole sky as the station orbit the Earth. But then, working out what the object is and locating it accurately is impossible unless you have some device that can continue to look at the source for some time and with higher resolution: something like Swift.

Thanks to a collaboration between these two instruments, within hours of the MAXI discovery Dr. Jamie Kennea, a Penn State scientist who leads the MAXI-Swift transient team, had triggered Swift observations of the source. Swift was built to respond rapidly to phenomena it discovers for itself, but it’s pretty cool that it can also respond so fast to phenomena one of its cousins finds.



Learn more about Swift:



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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.

*** 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-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 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.

star factory

MONDAY JULY 12: Washington Post weather blogger Andrew Freedman writes about a recent glacier retreat in NASA eyeballs glacial melt in Greenland. . . .  NASA Earth science storyteller Mike Carlowicz explained the science last week.

DEAD WEIGHT: Engineers at Goddard simulate the heavy load of instruments James Web Space Telescope will carry into deep space.

AWESOMENESS: NASA Blueshift‘s Weekly Awesomeness Roundup covers Hubble fireworks, renegade planets, a mind-blowing physics experiment in Germany, and other USDA Choice Scientific Beef of the week.

MARS ROCKS! Goddard’s Sciences and Exploration Directorate Chief Scientist James Garvin gives you a guided tour of Martian geology on WorldWideTelescope. Here’s the article in The Universe Today.

RABBIT HOLE: The Lunar Reconnaissance Orbiter unveils “rabbit holes” on the moon.

THREE’S A CHARM: On this day in 1961, NASA launched the Tiros 3 satellite. . . In 1960, Tiros 1 had taken the first-ever image of Earth from orbit. . . . Tiros stands for Television and InfraRed Observation Satellite, designed to test experimental television techniques and infrared equipment.

DUST-UP: A Space.com story about effects of lunar dust on equipment quotes Goddard planetary scientist William Farrell.

blooming ocean

TUESDAY JULY 13: What, ANOTHER fabulous Hubble Space Telescope image of a cosmic star factory? This one’s in the constellation Puppis, the poop deck of Jason’s fabled ship Argo from Greek mythology.

GRAB A SHOVEL: In today’s Systems Engineering Seminar, Warren Mitchell, Syed Hasan, and Jason Laing of the Goddard Flight Dynamics Facility recalled the drama of supporting the Space Shuttle Endeavour (STS-130) mission and the launch and operation of the Solar Dynamics Observatory (SDO) during the worst snowstorm in memory. Rani Gran’s account of Goddard’s Snowpocalyse adventure provides details.

MUMMA’s THE WORD: A video profile of astrobiologist Michael Mumma talks about the origin and evolution of life in the universe. . . . SAM I AM: And don’t miss the series of video profiles of Goddard researchers working on the Sample Analysis at Mars instrument package that will allow the Mars Science Laboratory rover to search for life signs.

OCEAN BLOOMS: The MODIS Image of the Day team posts a mighty fine satellite portrait of phytoplankton blooming in the North Sea.

TURN, TURN, TURN: A video made of GOES-13 satellite imagery tracks two weeks in the rip-roaring life of Hurricane Alex.

X-ray blast

WEDNESDAY JULY 14: NASA’s Swift observatory is temporarily blinded by the X–ray flash triggered by the explosion of a massive star morphing into a new black hole. . . . ME TOO! Gogblog profiles Phil Evans, the British investigator who uncovered the X-ray flash. . . . FAST WORK: PSU and gogblog post the story 10:58 am; Science NOW posts a “ScienceShot” news brief at 4:24 pm by astro-writer extraordinaire Ken Croswell. . . . LISTEN: “How a bright star fooled a top observatory into thinking it was unreal,” according to BBC Five Live presenter Dotun Adebayo. BUT WAIT, THERE’S MORE: The University of Leicester, where Phil Evans works, posts its own release on the blinding blast.

RED PLANET RENDEZVOUS: Forty-five years ago today, the Mariner 4 space probe flew within 6,118 miles of Mars after an 8-month journey. . . . MARINER 4 was the first spacecraft to take close-up pictures of another planet.

NEW TREND: Goddard Tech Trends releases its summer issue, featuring blacker-than-black nanotechnology and other innovations brewing at Goddard.

GULF OIL SPILL: NASA’s Aqua satellite scans the Gulf oil spill in a natural-color image.

planet or comet?

THURSDAY JULY 15: The late Dr. Timothy Hawarden receives a posthumous NASA Exceptional Technology Achievement Medal for developing innovative cooling techniques for infrared space telescopes — including the coming James Webb orbiting observatory.

SUPER-HUBBLE: Is it a planet? Is it a comet? No — it’s . . . . ANOTHER mind-numbingly interesting Hubble Space Telescope exoplanet discovery!

ORDER UP: According to a report in eWeek.com, Dell Inc. will sell Goddard’s NASA Center for Climate Simulation souped-up servers in a contract worth up to $5.1 million dollars . . . . The new servers will double NCCS’s computational capacity to more than 300 trillion calculations per second.

RUN THAT BY ME AGAIN: “The extreme tail loading and unloading observed at Mercury implies that the relative intensity of substorms must be much larger than at Earth.” Find out what Goddard space physicist James A. Slavin is talking about in a web feature about recent discoveries by the MESSENGER spacecraft.

ECLIPSE PORTRAIT: Like most earthlings, you probably didn’t make it to Easter Island to see the solar eclipse on Sunday July 11. But here’s something you would not have been able to see even from Easter Island: a combined space-and-surface view of the eclipse, created by Goddard media specialist and sun worshipper Steele Hill.

PLANKTON ON PARADE: The What On Earth blog posts the last of four dispatches from guest writer Karen Romano Young on the ICESCAPE expedition, “Plankton On Parade.”

man on the moon

FRIDAY JULY 16: Today in 1969, Apollo 11 blasted off at 09:32:00 am EDT from Launch Complex 39-A Kennedy Space Center in Florida for the first manned landing on the moon.

WoE OF THE WEEK: The What On Earth bloggers post the latest NASA Earth Buzz, with the top recent Earth science stories and the answer to the “What on Earth is THAT?” image quiz from last week. . . . ANSWER: soot particles from a wildfire.

WARM DATA: NASA’s Earth Observatory posts a global temperature anomaly map comparing readings for July 4–11, 2010, to the same dates from 2000 to 2008. Land surface temps come courtesy of the MODIS instrument aboard NASA’s Terra satellite.

HOT LINKS: The Physics Today website offers a feature story about NASA’s A-Train of satellites, Touring the atmosphere aboard the A-Train, by Tristan S. L’Ecuyer and Jonathan H. Jiang. “A convoy of satellites orbiting Earth measures cloud properties, greenhouse gas concentrations, and more to provide a multifaceted perspective on the processes that affect climate.”

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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.