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Majestic Saturn

The Cassini mission could well be one of the most successful space missions ever. It left Earth 11 years ago, and has been observing the planet Saturn since 2004, sending us back not just fantastic scientific data, but some images which can quite simply take your breath away. Cassini is now well into it's extended mission, Cassini Equinox, and I'm sure everyone's looking forward to seeing what else the little probe can send back to us...




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More full sized images and some more details are on Boston.com's The Big Picture.

Top 10 most interesting multiple star systems

There are lots of fascinating things out there in the cosmos. Galaxies, black holes, interstellar clouds and the like. Personally though, I just love stars. I guess that's why I decided to study them in more detail. Even the most mundane stars are fascinating when you look at them closely enough. But stars can be intricate and complex things, with eventful lives - especially when they're partnered with other stars. Not all stars live alone like the Sun does. A great many go around in pairs or even larger systems. These star systems are fascinating indeed, to professionals and amateurs alike. Without further ado, then, I present to you my own Top 10 most interesting multiple star systems!

(In no particular order.)



Albireo
A firm favourite among many amateur astronomers, Albireo (also known as beta-cygni) is actually a triple star system. Through a telescope though, it appears as a particularly beautiful visual binary -- a bright yellowish star with a fainter blue companion (shown here to the right). In 1976, astronomers at Kitt Peak discovered that the bright yellow star is actually a spectroscopic binary.

The two visual stars are around 380 light years away, and a huge 35 arcseconds apart. In other words, that fainter blue star (a fast rotating Be-class star) would take over 100,000 years to complete one orbit of the central binary -- assuming it's even part of the system.

Cygnus X-1
Cygnus X-1 is a very interesting little system. Discovered in 1964, it's one of the brightest x-ray sources in the sky, with a flux as high as 2.3x10^-23 janskys (if you don't know what a jansky is, suffice to say that's surprisingly bright).

In fact, Cyg X-1 is one of the most promising candidates in the sky for a stellar mass black hole, with around 8.7 solar masses compressed into an estimated 26km event horizon. In a tight binary orbit (around 0.2AU) around the black hole, a blue supergiant orbits once every five and a half days in a nearly perfect circular orbit. It is slowly being ingested, as stellar material is drawn towards the black hole, forming an accretion disk. As the inner parts of this disk are heated to millions of kelvins, the atoms start to emit the bright x-rays as seen from Earth. Around 6000 light years away, there's a fair chance it could be part of the Cygnus OB3 association, which would make the system around 5 million years old. The black hole may have once been a star over 40 solar masses in size.

The evidence for Cyg X-1 being a black hole is actually so good that Stephen Hawking once lost a bet against Kip Thorne, acquiescing in 1990 that it could only be a gravitational singularity!

16 Cygni
70 light years away, 16 Cygni is a trinary system. A Sun-like yellow dwarf with a close(ish) red dwarf companion orbiting 73 AU away. Further out, another, slightly smaller, yellow dwarf orbits the main pair. Further out, but no one's entirely sure how far exactly, it would seem. Estimates range from 860 AU to 15,180 AU, giving an orbital period of anywhere between 18,200 to 1.3 million years. Another good example of how a tiny change in the calculations and observations can have a dramatic effect in astronomy. The 16 Cygni system is estimated at around 10 billion years old (so quite a bit older than The Sun), and has one known planet. Orbiting the smaller of the two yellow stars is a massive planet in a close elliptical orbit.

Interestingly, 16 Cygni is one of a select few stars which has had messages beamed to it via METI. If there's anyone there to hear it, they should receive it in November 2069. Who knows... With all the messages being send out, we might even have a reply sometime over the next 200 years or so.

Kelu-1
Quite nearby at only 30 light years away, Kelu-1 was only discovered recently. The reason why is simply -- it's a vanishingly faint brown dwarf system. Discovered in 1997, Kelu-1 was one of the first known free brown dwarfs not to be tied to a larger stellar companion. Since then, it's been visually confirmed that there are actually two visible brown dwarfs in the system.

In 2008 though, it was found that actually, it's probably a trinary system, with the "larger" of the two stars actually being a spectroscopic binary. The central pair, Kelu-1Aa and Kelu-1Ab are difficult to discern, but the orbiting dwarf Kelu-1B is around 6.5 AU from them, completing an orbit once every 38 years or so.

Pismis 24-1
In a stark contrast to the tiny Kelu-1 system, Pismis 24-1 is one of the heaviest trinary systems known. Interestingly, it's in very much the same configuration, with a spectroscopic binary pair too close to properly resolve, and another star at a somewhat greater distance.

It's part of the Pismis 24 open cluster -- a collection of some of the most massive stars known Pismis 24-1 is the brightest star visible in the picture to the left. Before it was discovered that this star is actually a multiple star system, it was estimated at nearly 300 solar masses. A single star simply cannot form with such a high mass -- it would be above the Eddington Limit. As you can imagine, this baffled a few astrophysicists for a while. All the same, three stars each weighing in at around 100 solar masses is still rather immense, but at least it's explainable by theories!


Castor
Located in the constellation of Gemini, Castor is a hexuple star system. In other words, it contains a whopping 6 stars! Visually, you can discern two separate stars, but each of them is also a spectroscopic binary. Both of these are actually an A-class star with a red dwarf companion. Another, fainter, companion star to the system is quite a rarity, in that it's an eclipsing binary system composed of two red dwarfs.

Quite a big family, as stars go.

40 Eridani
Just over 16 light years away, the 40 Eridani system is the home of the first white dwarf ever discovered. It's an interesting system because that white dwarf would once have been the main star observable. As a white dwarf, it's now little more than a stellar corpse, left orbiting the stars that were once its underlings. It now revolves in an eccentric orbit around 35AU from a red dwarf flare star companion. These two both orbit 40 Eri A, a red-orange dwarf star, roughly 400AU away.

There's a fair chance a habitable planet could exist in the 40 Eridani system. The habitable zone around the main star is around 0.6AU away (more or less the same orbit as Venus around the Sun). The other two stars would have little influence on such a planet, appearing as a bright red and white pair -- not bright enough to illuminate the planet at night, but bright enough to be visible during the day (assuming an Earth-like atmosphere). They'd appear as roughly magnitude -8 and -6 white and reddish stars in the sky. To compare, Venus is around magnitude -4.7 at its brightest.

Polaris
Polaris is surely amongst the most famous stars in the sky. 430 light years away, it's been used by sailors in the Northern hemisphere for hundreds (perhaps thousands) of years to navigate by. In fact, Polaris is actually another trinary system. The primary star in the system is a yellow bright giant. It's orbited closely by a hard-to-see dwarf star at around 18.5 AU, and more distantly by an F-class main sequence star, a huge 2400 AU away. The optimist in me would like to point out that an F-class star with solar metallicity could well be host to a habitable planet or two, though it's hard to say how safe it is being so close to a variable giant!

Polaris is another star which is farily popular among amateur observers. It's a classic population I cepheid variable (actually the closest one to Earth), and though I've never looked at it myself, I've heard others say that with a good enough telescope, you can even make it out as a visual binary.

TV Crateris
150 light years distant, TV Crateris (also known as HD 98800) is an interestting little quadruple star system. Firstly, all four stars are T Tauri stars (young stars, still not properly formed) and secondly, they all appear to be sun-like stars. Two close binary pairs orbit each other at around 50 AU, and as you'd expect from a young star system, there's a big dusty accretion disk surrounding the central pair.

Excitingly though, that disk isn't constant. It has a big clearing. Specifically, it's made up of an inner disk from 1.5 - 2 AU and an outer disk that starts around 5.9 AU. A big gap in a ring like that could quite possibly be caused by planets, either fully formed or still accreting material. Which is a logical assumption -- dusty disks are often associated with planets. It could well be that we're seeing planet formation happening in this system. If we are, they're going to be brightly lit planets for any life that might someday live there...

Alpha Centauri
Including Alpha Cen is almost obligatory in this list! A trinary system, I've written about it before at great length, as have many others. With good reason. Frankly, our nearest stellar neighbour, at a mere 4.37 light years away, is quite an inspiring place -- if for no other reason than that it's almost certainly going to be the first extrasolar system the human race eventually visits.

Appearing as a single star to the unaided eye, Alpha Centauri is the third brightest star in the sky. With a telescope though, it makes for a very pretty visual binary. Dim little Proxima, the third star in the system, appears about 2.2° away from the central pair. If it were bright enough to be seen by the naked eye, you wouldn't even think it was part of the same system.

Standing on a rocky moon somewhere in the Alpha Centauri system might grant you a view a bit like this one...



Image credits (in order of appearance):
"Tatooine planet" - NASA JPL/Caltech
Albireo - Richard Yandrick
Pismis 24 open cluster - NASA, ESA and J. M. Apellániz
Alpha Centauri hypothetical planet - "The plague", Wikimedia Commons

8 reasons to be amazed by Gamma Ray Bursts!

Ok, so I have gamma ray bursts on the brain at the minute, which isn't unexpected after reading about them for a week. Besides, frankly, they're so damn fascinating! Seriously, the most dramatically powerful events in the known Universe, and we still don't know precisely what causes them. Just... fascinating. So to let some of this escape from my brain, here's 8 things about GRBs which may interest you...

1. There are "long bursts"...

Long bursts are widely believed to be a type of supernova event. In fact, some have been observed in association with a supernova (the first being GRB 980425). The process is suitably melodramatic. As soon as an extremely massive, fast rotating star burns enough fuel, it's core becomes so massive that it can't withstand it's own gravity. It collapses, in a similar way to a regular supernova, but it doesn't stop there. Because these stars are so massive, more and more stellar material is sucked into the core, collapsing it directly into a black hole. The star then proceeds to devour itself, releasing such vast amounts of energy that two beams of energy puncture the star at it's North and South poles. Think about that for a moment. Enough energy to puncture a star. A massive one at that!

It's one of these beams of intensely bright radiation that we see as a "Gamma Ray Burst".

2. ...and there are "short bursts"

Short gamma ray bursts are believed to come from something altogether different. While there are competing theories and diagreement, many believe that short bursts come from two neutron stars colliding. While neutron stars are so tiny, you might not expect them to ever come close enough to collide, don't forget that an average neutron star will be twice as massive as the Sun and have gravity to match.

If two neutron stars get trapped together by gravity, it's thought that they would slowly and inexorably fall together. As they rotate around each other, they would emit gravitational waves, losing energy and thus losing speed. With the loss of speed, they'd lose orbital distance. Eventually (probably over millions of years), they'd fall so close together that they'd crash into each other. The collision would be violent, but swift, emitting a brief but gargantuan belch of gamma rays before both stars collapsed into a silent black hole.

3. (Actually, there are other types too)

There's a third theory which is sometimes accepted as the cause of some gamma ray bursts. Megaflares.

One day before my 24th birthday in 2004, a blast of gamma radiation saturated every single gamma ray satellite in orbit. It was so powerful it even disrupted Earth's ionosphere. The source? A type of rare, highly magnetised neutron star, known as a magnetar. The specific one, SGR 1806-20, is one of only five known in our entire galaxy.

Whether megaflares could be the source of some GRBs or not is disputed, but one thing's for certain. A megaflare like the one in 2004 would be easily observable in another galaxy.

4. You can see them from halfway across the Universe

Gamma ray bursts don't just emit gamma rays. They also have an "afterglow" that covers the entire electromagnetic spectrum. X-rays and ultraviolet right the way down to infrared and radio waves.

In March 2008, one burst (GRB 080319B) was so bright that you would have been able to see it with the naked eye for 30 seconds. Despite a redshift of 0.937. Let's put that into perspective -- because of the way redshifts work, a redshift of 1 can be considered to be about halfway across the observable Universe. Loosely 7.5 billion light years away. This GRB was half a Universe away and visible to the naked eye! Incredible.

5. We've found one from shortly after the Universe was born!

The record holder for most distant object ever observed was a gamma ray burst. Just last month, GRB 090423 was picked up by the Swift satellite. It lasted about 10 seconds, and was measured to have a redshift of 8.2. Whatever caused it exploded roughly 13 billion years ago -- estimated at a mere 630 million years after the Big Bang. The Universe was just a baby back then. Even the galaxies were young that long ago.

Interestingly, seeing a GRB this old implies that massive stars were indeed forming and dying in the early Universe. It was probably stars like these that created the heavier elements that would eventually form cosmic dust, planets... and us.

6. We've known about them since the Cold War

We've actually known about gamma ray bursts since 1967. In 1963, the Partial Test Ban Treaty was drawn up to prevent the deployment of nuclear weaponry in outer space and the upper atmosphere (as well as under water). In order to monitor this, the US military developed Project Vela.

Instead of detecting nuclear weapons though, project Vela detected GRB 670702! After several more were observed, the Los Alamos National Laboratory published the paper Observations of Gamma-Ray Bursts of Cosmic Origin -- the first ever publication on GRBs. Since then, GRB research has blossomed into a research field in it's own right.

7. They're rather dangerous

Ok, that's an understatement. On the list of "Things which could cause the end of the world", GRBs are pretty high up there.

When we talk about GRBs, we're talking about something violent enough that we can see them from the other side of the Universe. Think about it. That isn't something you'd want to happen in your backyard. It's a worthwhile concern though. A nearby gamma ray burst would severely damage Earth's biosphere. Those gamma rays, much tougher than the worst solar flare imaginable, would fry the upper atmosphere. Nitrogen and oxygen would be forcibly reacted into nitric oxide, and nitric oxide is sadly rather good at destroying ozone. It's been calculated that a nearby GRB hitting Earth for just 10 seconds could destroy up to half of Earth's ozone. It would take at least five years for the ozone layer to recover, during which time ultraviolet from the Sun would play havoc with life on land.

Worryingly, it's even been considered that the Ordovician-Silurian extinction events 450 million years ago could have been caused by just such a gamma ray burst.

8. We're safe. For now. So we think.

GRBs are mercifully rare. Some estimate that just one burst will occur in the Milky Way every hundred thousand years to every million years. Others believe that bursts can only happen in galaxies with much fewer heavy elements than the Milky Way ("Metal-poor" galaxies).

Some astronomers were concerned for a while about a star named WR 104 (shown in this image here), an ageing massive star (known as a Wolf-Rayet star). The trouble is, we don't know enough about gamma ray bursts to say if this star could produce one. If it could, the star's rotational axis is aligned within about 16° of Earth which would make this a rather dangerous place to be living. Reassuringly, most now believe that WR 104 it isn't the "loaded gun" we once thought it was, and is unlikely to produce a gamma ray burst.

But there's no way we can really know for certain...

Didn't we have a lovely time, the day we went to Mare Tranquillitatis...

"Innovating is always risky and costly.
But if you don't do it,
you come to a standstill
and progress is halted."

I must say, I agree with Greg Fish's recent post over at World of Weird Things. In fact, I agree rather vehemently. I've bemoaned in the past, how human technology seems to be stagnating in many areas. Indeed, in that same rant almost a year ago, I drew reference to how the proposed Orion Spacecraft, part of NASA's Constellation program looked suspiciously similar to the, frankly, old fashioned space capsules that were used back during the early days.

Now granted, NASA have upgraded the design a bit since then, using newer technology. They're going to make them a little more spacious too, holding four to six astronauts. A definite improvement over the first space capsules. I've heard it said that the old Gemini spacecraft were so cramped that they weren't so much piloted as worn. But all the same, the fact remains that it's a capsule. A pressurised tin can. Quite a far cry from the feat of engineering that should be replacing the Space Shuttle's magnificent design. Instead, we're using new technology in an old design. A bit like rebuilding the Wright Brothers' plane and fitting it with satnav and radar. If you see what I (somewhat whimsically) mean.

I hasten to add that I'm not trying to be unduly critical. In fact, I'm a huge supporter of spaceflight, manned and unmanned. As a kid I used to eagerly anticipate the day when NASA might announce that they'd be sending people back to the Moon. My 10 year old daydreams would lead me to wonder what we might find, the day we finally made it to Mars. After all, we went to the Moon over ten years before I was born. Why shouldn't we be able to get to Mars within my lifetime. Sadly, that announcement never came. More and more often, people would speak wistfully of the days "when we went to the Moon", as if talking about a childhood holiday to Brighton or Lyme Regis. Where was the passion? Where was the drive to go back? To go further?

Unfortunately, now people are genuinely talking about going back, I find myself confused, wondering why they're using essentially the same methods they used 40 years ago. Don't get me wrong, here. Apollo worked. It worked quite successfully (despite early mishaps). A brand new 4-door family saloon car these days probably contains more sophisticated technology than those intrepid astronauts used to first set foot on the Moon, and I wouldn't dare belittle or diminish their achievement in any way. But... haven't we progressed at all?



Perhaps the thing I find most puzzling is exactly how much of this thing is going to essentially be disposable! The Saturn V that launched the Apollo missions was then, and still is now, the largest and most powerful launch vehicle ever constructed. The Constellation Program proposes to use not one, but two rockets per mission. One (Ares I) to carry the crew, and one (Ares V) to carry the cargo. Ares V will be by far and away the largest rocket ever. EVER. But really, in this age of recycling and conservation, is this really viable? Weren't we supposed to be working on fully reuseable spacecraft by now?

Spaceplanes were being developed. They were, until their budgets were cut, or their programs were cancelled. The X-33 and it's successor, the Orbital Space Plane should have been practically ready to fly by now. Instead, after investing hundreds of millions of dollars, the plugs were pulled, and these concepts were relegated to remain, simply, as concepts. The cancellation of the Orbital Space Plane was largely a reaction to the Space Shuttle Columbia disaster in 2003. Before the ill-fated STS-107, the Shuttles were deemed viable for use right up to about 2030. Afterwards, it was decided that an Apollo-style capsule would be safer for the crew. The days of the Shuttle were numbered.

Unfortunately, this leaves us having taken one step forward and two steps back. Recreating the Apollo missions seems to be the "safe" option, even inspite of the fact that the Apollo mission itself wasn't without its setbacks -- most notably, the catastrophe that was Apollo 1. Back then, that caused a major rethink and considerable reworking of the technology in order to prevent the same failure happening again. The result was that the remainder of the Apollo program (until it too was cancelled) was a resounding success (with one "sucessful failure"). Sadly, it seems that if the Apollo 1 incident happened tomorrow, it would probably see the cancellation of the entire Apollo program.