Are Brown Dwarfs More Common Than We Thought?

A brown dwarf plus aurorae (NRAO)

In 2007, a very rare event was observed from Earth by several observers. An object passed in front of a star located near the centre of the Milky Way, magnifying its light. Gravitational lensing is not uncommon in itself (the phenomenon was predicted by Einstein in 1915), but if we consider what facilitated this rare “microlensing” event, things become rather interesting.
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WR 104: Not The Killer It Used To Be

WR 104. A killer? Not so much.
WR 104. A killer? Not so much.

It’s interesting how astronomical harbingers of doom have the ability to pop up more than once on the ‘net. However, the doom isn’t quite as terrifying when you’ve sat through a conference presentation by a scientist who has exhaustively given every reason as to why this particular killer won’t hurt you.

Enter WR 104.

To be honest, if it wasn’t a Wolf-Rayet star, I probably wouldn’t be writing about it (as we all know, or you should know, Wolf-Rayets are my favourite stellar objects), but this little fact combined with the fact that I know the Earth is no longer on the WR 104 hit-list, I feel compelled to correct an article that has just popped up on the web referencing out-of-date source material.

So, let’s wind this back the clock to January 2009 when I sat in on a very reassuring this-star-isn’t-actually-going-to-kill-us-after-all astro presentation…
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Star Formation: The Game

starformation

Dave Mosher, I’m pointing my finger at you for this late night effort! Usually I stay up late to write articles, but for the last 30 minutes I’ve been playing this game after Dave sent a message on Twitter saying he had been playing a “simple” and “addictive” star formation game. No kidding! I shouldn’t have even clicked the link. But like a caffeine-infused moth to a super-shiny flame, off I went for some simple star-creation fun.

It looks like the Star Formation game is part of Discover Magazine’s featured article about the mysteries of star birth (it’s a great read, check it out). The game is simple, yet captivating (despite a few minor bugs). You play the role of supernova progenitor, dropping some massive star fury on an unsuspecting nebulous cloud of hydrogen. According to the game developers, the situation is physically accurate, it is just up to you to create the perfect conditions for stars to form in the dense cloud. It would appear the lectures I attended on star formation paid off, as I speak I’m on top of the leaderboard with a whopping 21122 points (see the screengrab above, I saved it posterity, I doubt I’ll be at #1 for much longer).

I’m all for games with an educational element, and I can’t think of a better way to spend an evening (well, I can, but if you’re stuck in the office, this is a great alternative to work). I’m off to create some more stars, check out Discover so you can do the same (just you try to knock me from the #1 slot!).

What Will Happen When the Sun Turns into a White Dwarf?

Strong tidal interactions are thought to shred any asteroids or comets as they get too close to a white dwarf (NASA)

All the way back in January, I had the great fortune to attend the American Astronomical Society’s (AAS) conference in Long Beach, California. I had a lot of fun. However, between the free beer and desperately searching for wireless Internet signal, I also did some work. During my travels, I spent some time browsing the poster sessions, trying to get inspiration for an article or two. You’d think that when presented with hundreds of stunning posters that inspiration wouldn’t be that far away. However, I was repeatedly frustrated by information overload and defaulted to a clueless meander up and down the pathways walled with intense science debates.

But then I saw it, right at the end of one of the poster walls, a question that got my imagination bubbling: “Will The Sun become a Metal Rich White Dwarf After Post Main Sequence Evolution?” The Sun? After the Main Sequence? Metal rich? To be honest, these were questions I’d never really pondered. What would happen when the Sun turns into a white dwarf? Fortunately, I had Dr John Debes to help me out with the answers…
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Small but Mighty: KPD 0005+5106, the 200,000K White Dwarf

Sirius B1 - one of the more famous white dwarf stars (Frank Gregorio)

A white dwarf called KPD 0005+5106 has been identified as the hottest star observed, ever. KPD 0005+5106 lives in the globular cluster M4, 7,200 light years away, and astronomers have always been intrigued by this stellar lightweight as its emissions have previously hinted it was quite toasty. Now, astronomers using data from the defunct NASA Far-Ultraviolet Spectroscopic Explorer (FUSE), have studied the white dwarf in more detail. KPD 0005+5106 emits radiation in the far-ultraviolet, indicating that its surface has a temperature of 200,000K. This is an unprecedented discovery, far-ultraviolet emissions are usually reserved for superheated stellar coronae. It may be small, but it’s a record-breaker
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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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