New Addition to the Exoplanetary Menu: The WASP-12b Sizzler

The hotspot: A very, very hot Jupiter has been discovered (ESA/C Carreau)
The hotspot: A very, very hot Jupiter has been discovered (ESA/C Carreau)

So how hot is the hottest known planet? Usually the temperature of a planet orbiting another star is of little concern to us. At the end of the day, are we really looking for an interstellar getaway? The chance that we’ll be colonizing any extra-solar planets in the near future is pretty low, but that won’t stop us from peering up the the heavens studying “Hot Jupiters” orbiting stars hundreds of light years away. However, astronomers have just discovered a planet I doubt we’ll ever want to visit. Enter WASP-12b, the hottest, and fastest gas giant ever observed…
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What Type of Star is Our Sun?

High-spatial and temporal resolution view from the Hinode SOT G-band filter (NASA)

Our Sun is often called an “average” or “unremarkable” star. This is a little unfair, after all this unremarkable specimen is responsible for generating all the energy for all the planets in the Solar System and it has nurtured life on Earth for the past four billion years. We are also very lucky in that the Sun (or “Sol”) is comparatively stable with a periodic cycle. What’s more, it is alone, with no binary partner complicating matters. We live in a very privileged corner of the Milky Way, within the “Goldilocks Zone” (i.e. “just right” for life – as we know it – to thrive) from Sol, where there is a unique and delicate relationship between our star, the Earth and interplanetary space. This is all great, but in the star club, how does Sol measure up? Is it really just an average, boring star?

I noticed in the comments of my article Observing an Evaporating Extrasolar Planet that some readers were discussing the classification of our Sun. This was in response to the subject of the exoplanet called HD 209458b orbiting the yellow dwarf star HD 209458 in the constellation of Pegasus. I happened to point out that HD 209458 was “…not too dissimilar to our Sun (with 1.1 solar masses, 1.2 solar radii and a surface temperature of 6000 K),” but also highlighted that HD 209458 was a yellow dwarf star. To be honest, I didn’t think about the connection until Jerry Martin asked why our Sun is never referred to as a yellow dwarf star? Helpfully, Dave Finton posted a link to Wikipedia that discusses this topic. For the full wiki treatment, have a look at Wikipedia:G V star, otherwise read on…

The Hertsprung-Russell diagram – stars plotted by their absolute magnitude, luminosity, classification, and effective temperature.

In the Hertzsprung-Russell Diagram, all known stars fall into one of six broad classifications depending on their luminosity and surface temperature. Observed stars can either be classed as (from big to small) a super-giant, bright giant, giant, sub-giant, main sequence or white dwarf. Within those classifications are spectral sub-classes from “O” (surface temperature of 30,000K), “B”, “A”, “F”, “G”, “K” to “M” (at 3,000K). However, for the sake of keeping this article on-topic, we’ll focus on our star, Sol (which is Latin for Sun).

Granted, our Sun has a surface temperature of around 6,000K, giving it a spectral classification of “G”. On the luminocity scale, our Sun scores a “V”. So, the Earth orbits a “G V star” which is otherwise known as a Yellow Dwarf star (although their actual colour ranges from white to slightly-yellow). Why is Sol considered to be “average”? That’s because in the Hertzsprung-Russell Diagram, yellow dwarfs can be found right smack-bang in the centre of the chart, half-way down the Main Sequence. Using this chart gives an idea about where our star came from and where it is going. For the moment, it is a hydrogen-burning star, converting 600 million tonnes of hydrogen into helium per second. This “hydrogen burning phase” generally lasts for about 10 billion years (Sol is about half-way through this phase) until all the hydrogen fuel is exhausted. When this happens, a yellow dwarf will puff up into a Red Giant, eventually shedding its outer layer, producing a planetary nebula. Eventually, the core will cool and compress into a long-living white dwarf star.

So, to answer the question, the Sun is a yellow dwarf star… and it certainly is not unremarkable

Recoiling Supermassive Black Holes and Stellar Flares

Simulation of black holes colliding. In a word, awesome (Max Planck Group)

Astrophysicists love to simulate huge collisions, and they don’t get much bigger than this. From the discoverers of the first ever observed black hole collision back in April, new observational characteristics have been researched and Max Planck astrophysicists believe that after two supermassive black holes (SMBHs) have collided, they recoil and drag flaring stars with them. By looking out for anomalous X-ray flares in intergalactic space, or off-galactic nuclei locations, repelled black holes may be spotted powering their way into deep space at velocities of up to 4000 kms-1
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Observing Red Dwarf Stars May Reveal Habitable “Super-Earths” Sooner

A planet orbiting a red dwarf (NASA)

OK, so if you’re an exoplanet hunter, which stars would you focus your attention on? Would you look at bright blue young stars? Or would you look at dim, long-lived red stars? If you think about it, trying to see a small exoplanet eclipse (or transit) a very bright star would be very hard, the luminosity would overwhelm any attempt at seeing a tiny planet pass in front of the star. On the other hand, observing a planet transiting a dimmer stellar object, like a red dwarf star, any transit of even the smallest planet will create a substantial decrease in luminosity. What’s more, ground-based observatories can do the work rather than depending on expensive space-based telescopes…
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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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The Crab Pulsar is Probed By LIGO. Is it Really a Smooth Neutron Star?

The Crab Nebula contains the famous Crab Pulsar (NASA/JPL-Caltech/R. Gehrz)

Scientists working with the Laser Interferometer Gravitational-Wave Observatory (LIGO) have announced their first land-mark discovery. LIGO was built to detect gravitational waves (as predicted by Einstein’s general relativity), but this discovery is actually about not detecting gravitational waves. Hold on, what’s all the fuss about then? This sounds like a null result, and in some ways it is. But on the other hand it may be one of the most important neutron star observations ever. So what has LIGO (not) seen?
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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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How Big is the Biggest Star in the Universe?

A comparison between the Sun and a hypermassive star. Credit: NASA

So how big is it? According to Fraser at the Universe Today, the largest known star is VY Canis Majoris. This is a massive star, otherwise known as a red hypergiant star and this one sits in the constellation Canis Major, about 5000 light years from Earth. Apparently it is more than 2100 times the size of our Sun, a monster! This star is so big that light takes more than eight hours to cross its circumference. In fact, this star, if placed in the centre of the Solar System, it would reach as far as the orbit of Saturn.

Although VY Canis Majoris is big, it isn’t as big as the biggest star could be. If it was cooler, a similar star could reach over 2600 times the size of our Sun…

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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How do you catch a Supernova in the Act? Build a Neutrino Detecting, Early Warning Device.

The massive star, Eta Carinae, explodes producing a huge pair of gas and dust clouds captured by the Hubble telescope. Image credit: NASA and Jon Morse, University of Colorado.

Observing a supernova as it happens is a very tough thing to do. If you blink, you’ll miss it. Astronomers are constantly trying to find ways to look in the direction of a massive star just before it blows, but supernova prediction is a very young science. Now, combining the sensitivity of neutrino detectors and attempting to make the data as “real time” as possible, the SuperNova Early Warning System (SNEWS) is born, sending you a neutrino weather forecast direct to your inbox hours before a star explodes.
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