A Powerful Galactic Explosion Has Been Detected — and Astronomers Aren’t Sure What Caused It

NASA/CXC/Pontifical Catholic Univ./F.Bauer et al.

A long time ago in a galaxy far, far away…

NASA’s Chandra X-ray Observatory has detected a mysterious explosion in deep space and, although astronomers have some suspected causes for the incredibly powerful event, there’s a possibility that it could be something we’ve never witnessed before.

The signal is the deepest X-ray source ever recorded and it appears to be related to a galaxy located approximately 10.7 billion light-years away (it therefore happened 10.7 billion years ago, when the universe was only three billion years old). Over the course of only a few minutes in October 2014, this event produced a thousand times more energy than all the stars in its galaxy. Before that time, there were no X-rays originating from this location and there’s been nothing since.

The explosion occurred in a region of sky called the Chandra Deep Field-South (CDF-S) — the event was therefore designated “CDF-S XT1” — and archived observations of that part of the sky by the NASA/ESA Hubble Space Telescope and NASA’s Spitzer space telescope revealed that it originated from within a faint, small galaxy.

“Ever since discovering this source, we’ve been struggling to understand its origin,” said Franz Bauer of the Pontifical Catholic University of Chile in Santiago, Chile, in a statement. “It’s like we have a jigsaw puzzle but we don’t have all of the pieces.”

One possibility is that we could be looking at the effects of a huge stellar explosion, known as a gamma-ray burst (GRB). GRBs are caused when a massive star implodes and blasts powerful gamma-rays as intense beams from its poles — think super-sized supernova on acid. They can also be caused by cataclysmic collisions between two neutron stars or a neutron star and black holes. Should one of those beams be directed at Earth, over 10.7 billion light-years of travel, the gamma-ray radiation would have dispersed and arrived here at a lower, X-ray energy, possibly explaining CDF-S XT1.

Alternatively, the signal may have been caused by the rapid destruction of a white dwarf star falling into a black hole. Alas, none of these explanations fully fit the observation and it could, actually, be a new phenomenon.

“We may have observed a completely new type of cataclysmic event,” said Kevin Schawinski, of ETH Zurich in Switzerland. “Whatever it is, a lot more observations are needed to work out what we’re seeing.”

So, in short, watch this space.

The research will be published in the June edition of the journal Monthly Notices of the Royal Astronomical Society and is available online.

Advertisements

Mystery Mars Cloud: An Auroral Umbrella?

The strange cloud-like protursion above Mars' limb (around the 1 o'clock point). Credit: Wayne Jaeschke.
The strange cloud-like protursion above Mars' limb (around the 1 o'clock point). Credit: Wayne Jaeschke.

Last week, amateur astronomer Wayne Jaeschke noticed something peculiar in his observations of Mars — there appeared to be a cloud-like structure hanging above the limb of the planet.

Many theories have been put forward as to what the phenomenon could be — high altitude cloud? Dust storm? An asteroid impact plume?! — but it’s all conjecture until we can get follow-up observations. It is hoped that NASA’s Mars Odyssey satellite might be able to slew around and get a close-up view. However, it appears to be a transient event that is decreasing in size, so follow-up observations may not be possible.

For the moment, it’s looking very likely that it is some kind of short-lived atmospheric feature, and if I had to put money on it, I’d probably edge more toward the mundane — like a high-altitude cloud formation.

But there is one other possibility that immediately came to mind when I saw Jaeschke’s photograph: Could it be the effect of a magnetic umbrella?

Despite the lack of a global magnetic field like Earth’s magnetosphere, Mars does have small pockets of magnetism over its surface. When solar wind particles collide with the Earth’s magnetosphere, highly energetic particles are channeled to the poles and impact the high altitude atmosphere — aurorae are the result. On Mars, however, it’s different. Though the planet may not experience the intense “auroral oval” like its terrestrial counterpart, when the conditions are right, solar particles my hit these small pockets of magnetism. The result? Auroral umbrellas.

The physics is fairly straight forward — the discreet magnetic pockets act as bubbles, directing the charged solar particles around them in an umbrella fashion. There is limited observational evidence for these space weather features, but they should be possible.

As the sun is going through a period of unrest, amplifying the ferocity of solar storms, popping off coronal mass ejections (CMEs) and solar flares, could the cloud-like feature seen in Jaeschke’s photograph be a bright auroral umbrella? I’m additionally curious as a magnetic feature like this would be rooted in the planet’s crust and would move with the rotation of the planet. It would also be a transient event — much like an atmospheric phenomenon.

The physics may sound plausible, but it would be interesting to see what amateur astronomers think. Could such a feature appear in Mars observations?

For more information, see Jaeschke’s ExoSky website.

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