Warning, Over-Hyped Title Alert: But It’s A Frackin’ SUPERNOVA!

I’m not kidding, last week was a huge mess of a supernova doomsday circus. It was like whispering “there’s a bomb under your chair” to the person next to you in a crowded theater and then watching the resulting flood of people slam into the fire escape. It was internet chaos. And there was no stopping it.

I am of course talking about the first, great doomsday scare of 2010: T Pyxidis.

Luckily for me, the first headline I saw was in the UK’s Telegraph that read “Earth ‘to be wiped out’ by supernova explosion.” Uh oh, that title sounds rather definite. Immediately, the bullshit sensor in my brain was tripped so I stopped flicking through the embarrassing excuse for a UK newspaper and had a read.

According to the article, some star (that I can’t pronounce) was “set to self-destruct” (as a big hairy supernova), a little over 3,000 light years away. Global chaos will therefore ensue. The ozone layer will be stripped away… and the Earth will be “wiped out.” (I still can’t work out how the Earth will be “wiped out.”)

I’m only picking on the Telegraph.co.uk as my skepticism knives were already sharpened after a series of idiotic woo-fueled articles (here, here and here) the website has played host to in recent months, but they weren’t the only news outlet to go batshit crazy with the “WE’RE ALL GONNA DIE” angle.

But who was really to blame for this mess? After all, the media was just the messenger, they must have gotten their lead from somewhere. Ah yes, the scientists… what did those guys really say?

You can find out how I got to the bottom of the science behind the hype in my Discovery News article “Will Earth ‘Be Wiped Out’ by a Supernova?” but cutting to the chase, it turns out that the scientists may have been a little hasty in their attempt to make international headlines.

As my mate Phil Plait mentions in his excellent write up (about my write up) of the T Pyxidis debacle on Bad Astronomy, this isn’t just a simple case of media hype, a lot of the blame should lay with Edward Sion et al. from Villanova University in Philadelphia.

Sure, some of the numbers didn’t add up (mistakes happen), but issuing a press release with a huge wad of inaccurate doom wrapped inside is pretty irresponsible. Have a read for yourself:

An interesting, if a bit scary, speculative sidelight is that if a Type Ia supernova explosion occurs within [that distance] of Earth, then the gamma radiation emitted by the supernova would fry the Earth, dumping as much gamma radiation (~100,000 erg/square centimeter) into our planet [sic], which is equivalent to the gamma ray input of 1000 solar flares simultaneously. –Excerpt from the Villanova press release, “THE LONG OVERDUE RECURRENT NOVA T PYXIDIS: SOON TO BE A TYPE Ia SUPERNOVA?”

“…fry the Earth”? Come on, that’s not even an accurate scientific term about what would happen if we were hit by a surge of gamma-rays. What’s wrong with saying “…the Earth would be at the receiving end of a Death Ray”? If you’re going to do the job of the tabloid press, hyping up your own research before the tabloid press has even read the release, you may as well be accurate.

And speaking of accuracy, my colleague Ray Villard was at the AAS and confirmed that Sion’s numbers were out by a factor of 10. “A supernova would have to be 10 times closer [to Earth] to do the damage described,” Ray said.

Although I was tough on the Telegraph in my Discovery News article (let’s face it, with an inaccurate and inflammatory title like that, they had it coming), in this case I think the main issue lies with Sion and co.

Why over-hype your research to get attention, when the research was interesting enough without declaring doomsday? By me even writing about the subject again, I think I just answered my own question.

But on a plus point, at least everyone knows what T Pyxidis is now…

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Whatever Happened to Hyper-Velocity Star HD 271791?

One scenario: Exploding star flings binary parter away at high velocity (Max Planck Institute for Astrophysics)

One scenario: Exploding star flings binary parter away at high velocity (Max Planck Institute for Astrophysics)

HC 271791 is a star with a problem, it’s moving so fast through our galaxy that it will eventually escape from the Milky Way all together. However, there is a growing question mark hanging over the reasons as to why HD 271791 is travelling faster than the galactic escape velocity.

So-called hyper-velocity stars were first predicted to exist back in 1988 when astrophysicist Jack Hills at Los Alamos National Laboratories pondered what would happen if a binary star system should stray too close to the supermassive black hole lurking in the galactic nucleus. Hills calculated that should one of the stars get swallowed by the black hole, the binary partner would be instantly released from the gravitational bind, flinging it away from the black hole.

This would be analogous to a hammer thrower spinning around, accelerating the ball of the hammer rapidly in a circle around his body. When the thrower releases the hammer at just the right moment, the weight is launched into the air, travelling tens of meters across the stadium. The faster the hammer thrower spins the ball, the greater the rotational velocity; when he releases the hammer, rotational velocity is converted to translational velocity, launching the ball away from him. Gold medals all ’round.

So, considering Hills’ model, when one of the stars are lost through black hole death, the other star is launched, hammer-style, at high velocity away from the galactic core. The fast rotational velocity is converted into a hyper-velocity star blasting through interstellar (and eventually intergalactic) space.

Hills actually took his theory and instructed the astronomical community to keep an eye open for speeding stellar objects, and sure enough they were out there. HD 271791 is one of these stars, travelling at a whopping 2.2 million kilometres per hour, a speed far in excess of the galactic escape velocity.

However, the 11 solar mass star didn’t originate from the Milky Way’s supermassive black hole (inside the radio source Sgr. A*), it was propelled from the outermost edge of the galactic disk. There is absolutely no evidence of a supermassive black hole out there, so what could have accelerated HD 271791 to such a high velocity? After all, stars aren’t exactly easy objects to throw around.

If HD 271791 used to be part of a binary pair, its partner would have had to suddenly disappear, releasing its gravitational grip rapidly. One idea is that HD 271791′s sibling exploded as a supernova. This should have provided the sudden loss in a gravitational field — the rapidly expanding supernova plasma will have dispersed the gravitational influence of the star.

However, according to Vasilii Gvaramadze at Moscow State University, the supernova theory may not be sound either; by his calculations a binary pair simply cannot produce such a large velocity. Gvaramadze thinks that a far more complex interaction between two binary pairs (four stars total) or one binary pair and another single star some 300 solar masses. Somehow, this “strong dynamical encounter” caused HD 271791 to be catapulted out of the system, propelling it at a galactic escape velocity.

Although this complex slingshot theory sounds pretty interesting, the supernova theory still sounds like the most plausible answer. But how could a sufficient rotational velocity be attained? As Gvaramadze points out, even an extreme rapidly orbiting binary pair cannot produce a star speeding at 530-920km/s.

This is in contrast to research carried out by scientists at the Max Planck Institute for Astrophysics and the University of Erlangen-Nuremberg. In a January 2009 press release, Maria Fernanda Nieva points out that this hyper-velocity star possesses the chemical fingerprint of having been in the locality of a supernova explosion. This leads Nieva to conclude that HD 271791 was ejected after its binary partner exploded. What’s more, a Wolf-Rayet may have been the culprit.

Up to now such a scenario has been dismissed for hyper-velocity stars, because the supernova precursor usually is a super-giant star and any companion has to be at large distance in order to orbit the star. Hence the orbital velocities are fairly modest. The most massive stars in the Galaxy, however, end their lives as quite compact so-called Wolf-Rayet stars rather than as super-giants. The compactness of the primary leaves room for a companion to move rapidly on a close orbit of about 1 day-period. When the Wolf-Rayet-star exploded its companion HD 271791 was released at very high speed. In addition, HD 271791 made use of the Milky Way rotation to finally achieve escape velocity. –Maria Fernanda Nieva

Even though Gvaramadze’s stellar pinball theory sounds pretty compelling, the fact that HD 271791 contains a hint of supernova remnant in its atmosphere, the supernova-triggered event sounds more likely. But there is the fact that just because this 11 solar mass star was near a supernova some time in its past, it certainly doesn’t indicate that a supernova was the cause of it’s high speed.

For now I suppose, the jury is still out…

Publication: On the origin of the hypervelocity runaway star HD271791, V.V.Gvaramadze, 2009. arXiv:0909.4928v1 [astro-ph.SR]

Original source: arXiv blog

Wolf-Rayet Star: My Favourite Stellar Object

Artist impression of a Wolf-Rayet star (NASA)

Wolf-Rayet (WR) stars are my favourite stellar objects bar none. Due to the excitement factor I find them even more interesting than black holes, pulsars and quasars. Why? Well, they are a significant period of a massive star’s lifetime making its violent, self-destructive death, possibly culminating in a supernova or gamma ray burst (GRB). WR stars blast out dense stellar winds creating a bubble of matter that completely obscures the star’s surface from any attempts at observation. They are also very noisy neighbours, disrupting binary partners and messing up huge volumes of space. If you thought a star might die quietly, the WR phase ensures this isn’t the case and astronomers are paying attention, making some of the most detailed observations of WR stars yet…
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Collapsing Wolf-Rayet Stars and Inverse Compton Scattering of Stellar Photons

A Wolf-Rayet star WR124 with surrounding nebula M1-67 (NASA)

Wolf-Rayet stars are a violent and self-destructive phase of a massive star’s lifetime. This is the point at which they begin to die as a prelude to a supernova and black hole formation. Often, large nebulae can be found around these bright stellar objects (pictured), emitting strong ultraviolet radiation. As Wolf-Rayet (WR) stars continue to lose huge amounts of mass and deplete all their fuel, they become even more unstable, resulting in a huge supernova. Exploding WR stars have been linked with powerful gamma ray (γ-ray) bursts; in fact the largest, most distant GRB was observed on March 19th in the constellation of Boötes by NASA’s Swift Observatory and the Polish “Pie of the Sky” GRB detector. There is some evidence that this GRB was the result of a WR star/neutron star binary pair, but what would happen if a WR star is sitting close to an O-type star just as it explodes?

As the WR star collapses, a shock wave (containing hot, relativistic electrons) sent hurtling toward the O-type star may cause inverse Compton scattering of the stellar photon field, generating powerful, long period emissions of γ-ray radiation. New research suggests that this mechanism may explain the 1-100 GeV γ-rays observed minutes or hours after the main GRB…
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Could a Wolf-Rayet Star Generate a Gamma Ray Burst?

Gamma ray bursts (GRBs) are the most energetic events to be seen in the observable universe. On March 19th, a record breaking GRB was observed in the constellation of Boötes by NASA’s Swift Observatory and ground based telescope arrays (i.e. the Polish “Pie of the Sky” GRB detector). This was an explosion unparalleled with anything we have ever seen. Not only was it the brightest GRB, it was the most distant GRB – this explosion occurred 7.5 billion years ago (it was therefore located 7.5 billion light years away). Taking measurements of the spectrum of light from these events not only helps us understand what causes such a massive detonation, but also reveals the nature of the Universe when it was half the age it is now.

In a new publication headed by the University of Utrecht, in The Netherlands, the highly dynamic and self-destructive Wolf-Rayet star has been singled out as a possible GRB progenitor after some complex tidal interactions with a binary partner, spinning-up the star until it collapses and unleashes vast amounts of energy into space…
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