Astronomers using the Chandra X-Ray Observatory may have found evidence for a young black hole: it was born in a titanic explosion just 31 years ago.

Black holes form when massive stars explode. The core of the star collapses, and if it’s massive enough (more than about 3 times the mass of the Sun), the gravity of the core can crush it down into a black hole.

Enter Supernova 1979c, a star that exploded in the nearby galaxy M100. About 50 million light years away, M100 is a lovely face-on spiral galaxy in the constellation Coma Berenices. SN1979c was discovered in — duh — 1979, and has been heavily studied for years since it was so bright, making it easy to see.

SN1979c was an interesting event, even for something as mind-numbingly violent as a supernova. The star that exploded was right on the edge of being massive enough to create a black hole; the total mass of the star was about 20 times the mass of the Sun, with a core of just about 3 solar masses. The question is, was the star big enough to create a black hole, or would the core collapse to form an incredibly dense neutron star?

Chandra observations may have answered this question. (more…)

What happens when a star with a planetary system (or perhaps a close stellar companion) gets old, expands into a red giant, and engulfs its neighborhood?

This:

"This", in this case, is the star BP Piscium (or just BP Psc), a star a bit less than twice the mass of the Sun located about 1000 light years away. The picture is actually a composite of both an optical image from the Lick Observatory (in white and green) and X-rays using the orbiting Chandra Observatory (purple).

The jets of matter streaming away are usually seen around young stars. When a star forms, there is a thick disk of material surrounding it. Due to processes not fully understood yet (though we know it has to do with the disk, the star’s spin, and the star’s magnetic field), matter and energy can be focused into those two beams, and they can blast away from the star’s poles at high velocity, stretching for several light years.

But there’s a monkey in the wrench here: BP Psc isn’t a young star.
(more…)

Some 60 million light years from Earth is the monster galaxy M87. It’s a massive elliptical galaxy, one of the largest such in the nearby Universe… if you count 600 quintillion kilometers away as "nearby".

And when it comes to the Universe, I do.

It sits in the center of the Virgo cluster, a collection of roughly 1500 galaxies all bound to each other by gravity. At the heart of M87 is one of the biggest black holes ever seen: something like 6 billion times the mass of the Sun (the Milky Way has one as well, but it’s a paltry 4 million solar masses). It’s called a supermassive black hole, and it’s active. That means it’s a sloppy eater: as matter falls in to the hole, it piles up outside and forms a giant disk, which gets hot… millions of degrees hot. The tremendous heat and other titanic forces join up to blast away a huge amount of the otherwise incoming material. It’s not a nice, neat process, and when a black hole on that scale lets out a belch, it’s felt for hundreds of trillions of kilometers… as you can see in this image:

[Click to supermassivize.]

This is a composite of two images, one taken in radio wavelengths by the Very Large Array (in red) and the other in X-rays by the orbiting Chandra Observatory (in blue). The X-rays are being emitted by gas blasting away from the black hole, heated up by the disk and the magnetic fields affiliated with the hole itself. The radio waves are from gas that previously existed outside and farther away from the black hole, which is being slammed into, stirred up, and swept away by the outflowing gas.

(more…)

Type Ia supernovae are very important exploding stars. It’s thought that this particular type of supernova has a very special property: they all explode with about the same energy. This makes them very valuable, because it means that if you can simply measure how bright they appear to be, you can figure out how far away they are. It’s like seeing headlights on the highway; dim ones are far away, and bright ones are close.

Of course, in reality, it’s not that easy. But after a Herculean effort, astronomers in the late 1990s figured they had been able to account for any small differences in brightness and could use these stars as "standard candles", benchmarks to calculate cosmic distances. Because they’re so bright, they make great milestones because they can be seen pretty much all the way to the edge of the observable Universe.

The thing is, it’s not clear how a type Ia actually forms. There are two models, both involving white dwarfs. These are the ultradense remnants of dead stars, the exposed cores of stars after they shed their outer layers. The Sun will one day be a white dwarf (in about 6 – 7 billion years, so don’t hold your breath). Because of complicated quantum physics, it turns out that white dwarfs can only have so much mass; if they exceed about 1.4 times the mass of the Sun they can collapse, either forming an even denser neutron star, or exploding as a supernova.

The first model of a Type Ia is a white dwarf orbiting a star like the Sun. The intense gravity of the dwarf draws material off the normal star, a process called accretion. The matter piles up, the mass limit is exceeded, and BANG! Supernova.

Well, it’s a lot more complicated than that, but close enough.

The second idea is that you have two white dwarfs orbiting each other. Over time they spiral in (this time due to relativistic effects called gravitational waves), get too close together, merge, and BANG! Supernova.

Astronomers have always assumed that the accretion scenario is the far more common of the two, because it takes a long time for two dwarfs to merge, whereas accretion can happen easily if a dwarf happens to be paired up with a normal star (which should be pretty common). But how do you tell which is which?

It turns out that the two different scenarios leading up to the explosion have two very different effects: accretion makes a lot of X-rays, while a merger does not. So astronomers did what you’d expect: they pointed the Chandra X-Ray Observatory at a bunch of galaxies and observed supernovae. What they found was pretty surprising: the amount of X-rays from Type Ia supernovae in nearby galaxies was 30 – 50 times lower than what would be expected from accretion. In other words, their observations strongly favor the idea that it’s the merger of white dwarfs that cause Type Ia supernovae.

Well! I was pretty surprised to hear that. Like other astronomers, I figured it was accretion that was the culprit. Now mind you, there are some caveats here. They observed elliptical galaxies, which tend to have an older population than spirals, so you might see more mergers than accretions. Also, it’s possible things were different in the past, and when we observe very distant galaxies were seeing them as they were billions of years ago.

But still, you just don’t expect to see what the astronomers saw, so it seems to me like they’re on to something here.

This has some interesting ramifications. It certainly affects a lot of fields of astronomy, like how binary stars form and change over time. But it may also affect cosmology, the study of the birth, evolution, and eventual fate of the Universe itself. If Type Ias are caused by a different scenario than previously thought, could it mean that our measurements of the distant Universe are wrong?

I asked this question specifically at the Chandra press conference, and was told that the two different scenarios produce explosions with pretty much the same energy, so this may only affect cosmological measurements a small amount. However, right now our theoretical models of the merger scenario are still pretty rough, so it’s unclear if the peak brightnesses of the two models are the same.

This may affect our measurements of dark energy, the mysterious pressure that seems to be accelerating the expansion of the Universe. My gut reaction is that this won’t matter a huge amount, since we have lots of independent ways of measuring dark energy, and they all appear to be in rough agreement. But this means we have one more thing to take into account in those measurements. And it may prove to be useful; if we can distinguish between the two supernova generators, our measurements will get that much more accurate.

I have to say I’m pleased with this; I studied supernovae in college and grad school, eventually studying one for my PhD (though it was of an entirely different flavor from this kind). I remember reading a long technical paper about the different Type Ia scenarios back then: it’s been a mystery for a long, long time. But with perseverance, the right equipment, and more than a touch of cleverness, we’re a big step closer to figuring this all out!

Related posts:
Fireworks and Pinwheels (an overview of Type Ia supernovae)
Dark Energy site open for business (explaining dark energy)
The Universe is 13.73 +/- .12 billion years old
What astronomers do (about the discovery of dark energy)
The cosmological not-so-constant

Image credits: NASA, ESA, The Hubble Key Project Team, and The High-Z Supernova Search Team, and NASA/CXC/M.Weiss (adapted a bit by The Bad Astronomer)

Deep in the heart of a globular cluster orbiting an elliptical galaxy, it looks very much as if a massive black hole is in the process of tearing apart and devouring the remnant of an old star. And how do we know we’re witnessing this violent stellar demise? Black holes are messy eaters.

The discovery comes from the Chandra Observatory, a telescope in space designed to detect X-rays. This high-energy form of light can only be generated by violent events, things like exploding stars, strong magnetic fields, or extremely hot objects. Astronomers (including Jimmy Irwin, an old friend I went to grad school with!) using Chandra detected an unusually bright source of X-rays coming from a globular cluster — a tightly packed collection of stars — belonging to NGC 1399, a galaxy 65 million light years away. In the picture above (a combination of Chandra X-ray images and optical images from the huge Magellan telescopes in Chile), the galaxy is the bright blob on the right, and the new object — called a ULX for Ultra Luminous X-ray source — is marked with the red lines.

We know black holes exist in globular clusters, so that’s nothing new. We also know stars are so jam-packed in globulars that it’s not only possible but relative common (on a cosmic scale) for these stars to interact gravitationally. When a star gets too near a black hole, it can have matter pulled from its surface, which falls into the black hole. As it plummets to its death, it can first pile up just outside The Point of No Return, whipping madly around the hole, and heating up so violently it can emit X-rays.

That sort of thing has been seen before. What’s new here is that first, the type of X-ray emission seen from this event indicates that the star isn’t simply giving up matter slowly to the black hole; it’s actually getting torn apart, physically shredded by the vast gravity of the black hole. Second, what the astronomers have seen is that the emission is rich in the element of oxygen, but oddly missing hydrogen. Hydrogen is the most common element in the Universe, and all normal stars are almost entirely made of the stuff (the Sun is, for example). Not seeing it means the star getting eaten up by the black hole is most likely a white dwarf, the dense remnant of a dead star’s core. After a lifetime of fusing hydrogen into helium, there typically isn’t any hydrogen left in a star’s core. Once the star dies, the remaining core becomes a white dwarf, devoid of hydrogen but also commonly rich in oxygen.

So not only is this possibly the first time a black hole has been caught in the act of viciously ripping a star apart, the star itself is a bit of an oddball.

And there’s more, too. Looking at spectra taken of the object reveals how fast the material is moving as it orbits the black hole, and that in turn tells us how massive the black hole is. What astronomers found is that this particular black hole must have a mass of a thousand times that of the Sun! Because of the way black holes form, it’s common to see them have a few times the mass of the Sun, or even as much as 20 or so. We also see truly gigantic ones with millions or billions of times the Sun’s mass. But it’s recently been theorized that intermediate-mass black holes exist as well, with hundreds or thousands of times our Sun’s mass. Observations have been tantalizing about these objects, and this new evidence from Chandra adds to the idea that middle-weight black holes exist.

I think observations like this are very exciting. When a new type of object is suspected, or even found, we usually get incremental supporting evidence for them. But it’s rare to get a twofer: not only does this support the existence of intermediate mass black holes, but we caught one in the act of violently tearing apart its dead neighbor. In a hundred years or so, the last morsels of the white dwarf will fall into the black hole, never to be seen again. Not even crumbs will be left, so it’s pretty cool we were able to see this when we did.

The 130th Carnival of Space blog roundup is being hosted by the Chandra blog. Yes, that Chandra. So go there and put your tax dollars to work.

When Galileo first turned his telescope to the sky, almost exactly 400 years ago, he could not possibly have known what he was starting.

Today, four centuries later, we’ve come a long, long way. To celebrate the anniversary of Galileo’s telescopic revolution, NASA’s Great Observatories — Hubble, Spitzer, and Chandra — have released a jaw-dropping mosaic of the very heart of the Milky Way galaxy. Behold!

[Oh yes, you want to click to embiggen that-- what I show here is a very compressed version. Or you can go here for a massive copy. You can also get wallpaper versions here.]

This image is nothing less than a heroic effort of astronomical artistry. It’s a chunk of the sky 38 x 14 arcminutes across, or about half the size of the full Moon, and it’s aimed right into the core of our galaxy. See the bright spot just to the right of the center? Buried in there behind light years of dust and gas is the monster of the Milky Way, a black hole with four million times the mass of the Sun. But even that is dwarfed by the 400 billion solar mass heft of the entire galaxy.

There is so much going on in this image it’s hard to know where to start. But first… the Hubble images are in the near-infrared, with a wavelength a little more than twice what the eye can see (1.87 microns for those playing at home). That’s represented in the image as yellow. Spitzer contributed observations in four infrared wavelengths (3.6, 4.5, 5.8, and 8.0 microns), and those are depicted in red. Chandra sees X-rays which are normally written as units of energy, but to remain consistent with the other two images, they were at wavelengths of 0.0005, 0.00025, and 0.00016 microns, and are shown in blue.

What does all this mean? Different objects emit light at different characteristic wavelengths. Warm dust, for example, emits strongly in the infrared. Stars and warm gas emit visible and near-infrared light. Violently heated gas, affected by huge magnetic fields or shocked by colossal collisions glows in X-rays. So this image is a polychromatic view of the crowded downtown region of a bustling city: our galaxy.

You might want to look at an annotated version of this image so you can get your bearings. It’s worth it!

The huge arches of gas on the left are actually the edges of gigantic molecular clouds (dense nebulae where stars are born), lit up by the torrential blast of light from a clutch of massive stars nearby. This clot of stars, called the Arches Cluster due to the arcs it excites, can be seen as a small spot glowing blue just to the left of center in the picture. Don’t be deceived by its diminutive appearance: the Arches cluster has thousands of superstars in it, each dwarfing our Sun, and each capable of sleeting out vast amounts of radiation that lights up the gas surrounding it. Were this cluster much closer than its 25,000+ light year distance, it would blaze in our sky like a beacon. Replace the Sun in our solar system with just one of those stars, and the Earth would be fried beyond the capability of any life to survive. You might as well try living in the flame of an arc-welder.

Below and just to the left of the Arches is a clumpier, more twisted arc of gas called the Sickle. That’s a giant cavity being carved out of dense gas by the Quintuplet cluster, the pinkish glow in its center. It’s another nursery of stars like the Arches cluster, which is also blasting out light and stellar winds which eat away at the gas enveloping it. The Pistol Star resides there, perhaps one of the most massive stars in the Milky Way.

And there’s more! The blue glow on the left is from an X-ray binary called 1E1743.1-2834, what is probably a massive star being orbited by either a neutron star or a black hole. Matter is being stripped from the star and piling up outside the collapsed companion, where it gets heated up to millions of degrees and emits X-rays.

Supernovae remnants dot the image, as do stars, filaments of gas, clouds of dust, and more. This picture is an astronomer’s dream, a map of everything someone might want to visit with a starship — as long as the shields are at full strength. This image is also a map of violence, turbulence, and unrest… a typical scene, so we think, of any normal spiral galaxy like ours. And our Galaxy’s center is considered quiet by astronomers! Some are far worse.

But this is home for us. It’s a place of unimaginable fury but also astonishing beauty… and we see it now as we do because we have dared to examine the world around us, to use tools we invent to peer closer, to magnify the tiny, to extend our eyes into realms we once didn’t even know existed. And every time we do — every single time — we find more questions, more puzzles, more things to examine.

And we find art. Galileo wasn’t the first to turn his telescope to the sky, nor was he the first to record what he saw. But he was the one who made everyone see what he did, and for that, all these years later, he is owed a debt of gratitude.