Supernova!



February 23, 2012 at 11:52 am | Leave a Comment

A Quarter-Century Perspective on 1987a

Supernova 1987A, in the Large Magellanic Cloud, a nearby galaxy. Astronomers in the Southern hemisphere witnessed the brilliant explosion of this star on Feb. 23, 1987. Shown in this NASA/ESA Hubble Space Telescope image, the supernova remnant, surrounded by inner and outer rings of material, is set in a forest of ethereal, diffuse clouds of gas. This three-color image is composed of several pictures of the supernova and its neighboring region taken with the Wide Field and Planetary Camera 2 in Sept. 1994, Feb. 1996 and July 1997. Courtesy Hubble Heritage Team (AURA/STScI/NASA/ESA).

It had to have been quite an exciting thing for Ian Shelton and Oscar Duhalde when they first saw a brightening star on a photographic plate that hadn’t been there night before.  Or, for Albert Jones of New Zealand, and Rob McNaught in Australia, who saw the same brightening and must have wondered “What??!”.  In Chile, Ian stepped outside the Las Campanas Observatory in Chile to visually check that area of the sky. Sure enough, there was a hugely bright star in the Large Magellanic Cloud that wasn’t that bright the night before.  All three observers had discovered the supernova of the century, named Supernova 197a.  It was the last explosive gasp of the dying blue supergiant star Sanduleak -69° 202 (called the “progenitor star”), and an eye-opener for scientists studying supernovae, particularly a type called “core collapse” or Type II.

When massive stars like the one that died to form Supernova 1987a come to the ends of their lives, they have basically run out of fuel to consume in their cores.  Stars begin by fusing hydrogen to helium in their cores. The result is heat and light.  Eventually the star runs out of hydrogen as fuel, so it begins to fuse helium, then carbon, and so forth, until it gets to iron.  At that point, fusing iron takes more energy than the process can put out, and that’s when the fusion action stops. Dead. And, there’s no way that the core can support the mass of the layers above it. So, it collapses.  The outer layers collapse, too, and when they hit the core, they rebound out, forming a huge shock waves that blows everything but the core out into space. That’s what we detect as a supernova.

Hubble images show the sequence of ring expansion around Supernova 1987a. Courtesy Mark McDonald via Creative Commons Share-Alike License.

Supernova 1987a was immediately surrounded by an expanding ring of debris.  Astronomers immediately began looking for that ring, and eventually the Hubble Space Telescope took images and data of it a few years later.  Today, 25 years after the first detection, astronomers are still watching the debris expand. As it does, it collides with material (gas and dust clouds) that the star shed earlier in its death process. When the shock wave and expanding debris make contact with that material, everything lights up.

Supernova 1987a has given astronomers new insight into the types of stars that become Type II supernovae.  For one thing at the time of Supernova 1987a’s discovery,  blue supergiants were not considered likely supernova candidates for a variety of reasons. Yet, here was one exploding in a supernova. So, astronomers had to go back and re-examine their ideas and theories about these kinds of high-mass stars.

For one thing, the progenitor star, Sanduleak -69° 202, just wasn’t on people’s radar as a possible supernova candidate. It didn’t show any hints that it was about to blow itself up. That raises a lot of questions about what we know of high-mass stars and their death cycles.

A composite image of supernova 1987a taken 20 years after the explosion was first detected. Data came from NASA's Chandra X-ray Observatory and Hubble Space Telescope. The outburst was visible to the naked eye, and is the brightest known supernova in almost 400 years. This shows the effects of a powerful shock wave moving away from the explosion. Bright spots of X-ray and optical emission arise where the shock collides with structures in the surrounding gas. These structures were carved out by the wind from the destroyed star. Hot-spots in the Hubble image (pink-white) now encircle Supernova 1987A like a necklace of incandescent diamonds. The Chandra data (blue-purple) reveals multimillion-degree gas at the location of the optical hot-spots. These data give valuable insight into the behavior of the doomed star in the years before it exploded. Credit: X-ray: NASA/CXC/PSU/S.Park & D.Burrows.; Optical: NASA/STScI/CfA/P.Challis

The progenitor star was a very compact and blue; not the kind of star to explode like this. So, there had to be another influence. It turns out there was more than one star involved; this system was a binary. One idea is that both the progenitor star and its companion were engulfed in an envelope of material.  The companion may have dissolved in some way, and that affected the progenitor star, and helped send it down the road to supernova-hood.  There are other explanations, and current and ongoing studies of the supernova remmants and the immediate neighborhood may help solve the mystery of why a blue supergiant exploded as it did.

Once the explosion DID occur, aside from the shock wave and light, there was also a huge burst of neutrinos — fast-moving particles that whiz across space.  One expert estimated that 1057neutrinos were generated by the explosion, speeding away in all directions. A few of them hit Earth and were detected by the Kamioka experiment in Japan, and by detectors in Cleveland and the former Soviet Union.

All in all, only 19 neutrinos were detected from 1987a, but they told astronomers a story of core-collapse inside a massive star. They also suggest that a neutron star formed in the wake of the core collapse of the supernova 1987a progenitor star. As of today, that neutron star has yet to be observed. There are a number of reasons for that, including the formation of a black hole at the same site.  Astronomers are still looking.

So, 25 years after the appearance of Supernova 1987a, there’s still something to study.  The continued expansion of the shock waves and debris rings into the surrounding material in interstellar space will provide much data about the material and those interactions. The search for the neutron star (or whatever’s left of the progenitor star), continues. And, astronomers continue to use this event to bolster and tweak theories about massive stars and their ultimate ends. It’s been a fascinating quarter-century, and the data continues to flow.  No doubt Hubble Space Telescope and ESA’s Herschel Space Observatory will continue to watch this object, as will the other facilities (such as Gemini Observatory) around the world. It will likely be a target for James Webb Space Telescope. So, stay tuned for new images and data to mark the 25-year mark of this cosmic event. Supernova 1987a might have exploded, but it’s not dead yet.

 

 

 

 

 

 





It Was 82 Years Ago



February 18, 2012 at 16:24 pm | Leave a Comment

The Rise of the Dwarf Planets

A Hubble Space Telescope image of Pluto (central object) and its four largest moons, Hydra (upper left), Charon (lower left), Nix (lower right), and P4 (upper right). Courtesy NASA/ESA/STScI.

February 18th is the 82nd anniversary of the discovery of Pluto, the dwarf planet.  The find was made in 1930 by an observer at Lowell Observatory in Arizona by the name of Clyde Tombaugh.  He had spent months searching through and comparing photographic plates of the sky, looking for a possible new planet. His discovery was confirmed, and the name Pluto was bestowed on March 24, 1930.  I had the pleasure to meet Clyde at a conference some years ago, when he spoke enthusiastically about his work to uncover this distant, frozen world.

Pluto is classified as a dwarf planet — which means it’s a special class of planet, much as white dwarfs are special classes of stars, and some galaxies are termed “dwarfs” based on the characteristics that differentiate them from spiral, elliptical, and irregular galaxies.

One of the fascinating things (among many) about Pluto is that its discovery really opened up a new phase of solar system exploration, resulting the discovery of more dwarf planets  in the outer solar system.

Granted, we’ve done quite a bit of solar system exploration since Clyde’s momentous discovery.  We’ve sent probes to most of the other planets, and studied them with ground- and space-based telescopes.  But, until recently, we didn’t have the technical wherewithal to do more than study Pluto from Earth (or Earth orbit, with Hubble Space Telescope, for example).  That changed when the New Horizons spacecraft was launched in 2006 on an voyage of exploration of the outer solar system.

New Horizons will arrive at Pluto in 2015.  It will study the planet’s atmosphere, surface characteristics, and its nearest moons.  After that, it will continue out to other outer solar system objects — in fact, its larger mission is to study the Kuiper Belt, a region of space that extends out from the orbit of Neptune and in which Pluto orbits .  It’s really the gateway to all the outer solar system worlds, including Pluto.

I mentioned that astronomers have found other icy worlds out in Pluto’s domain, and beyond. Eris is the most massive known dwarf planet (so far), and orbits the Sun out well beyond Pluto.  It’s an icy world roughly the size of Plut0. Then, there are Makemake, Haumea, Charon, Orcus, Quaoar, and Sedna.  They’re all smaller and more distant than Pluto, but there’s no doubt they’re worlds in their own right. Undoubtedly others are out there, making trans-Neptunian space a sort of new frontier.  This is why I see Pluto’s discovery as momentous. So, in celebration of Pluto Discovery Day, I raise a toast to Clyde Tombaugh — whose ashes are aboard the New Horizon spacecraft bound for Pluto space.  Not only did he discover a dwarf planet, but he also opened the gates to discoveries in a sector of the solar system once thought empty and barren.  It’s a bigger solar system than we thought, folks, and we have visionaries like Clyde to thank for helping us figure that out.





Attention, Luminous Blue Variable Fans!



February 16, 2012 at 11:19 am | Leave a Comment

More Outburst Data from Eta Carinae

There’s an unstable star out there that’s on the brink of destruction. It lies some 7,500 light-years away, embedded in a star-forming region called the Carina Nebula. The star itself is called Eta Carinae (Eta Car, for short), and it’s actually a double star system. Some 170 years ago, observers noticed that it was growing very bright. Over time, it became the second-brightest star in the sky.

This unexpected brightening came to be known as the “Great Eruption”, and astronomers of the time watched it with great interest — but didn’t have much in the way of sophisticated instrumentation to really dig into the object to tell what was going on there.  Today, modern telescopes are showing us what really happened during the Great Eruption.

The story goes like this:  the more massive member of the duo — a type of star called a luminous blue variable — began blasting out huge amounts of its own mass. Over the period of 20 years that it was seen to be erupting (from 1837 to 1858), this heaving star lost more than 20 solar masses of material.  Much of that “star stuff” can still be seen in a double-lobed cloud surrounding the system.

These images reveal light from a massive stellar outburst in the Carina Nebula reflecting off dust clouds surrounding a behemoth double-star system. The color image at left shows the Carina Nebula, a star-forming region located 7,500 light-years from Earth. The massive double-star system Eta Carinae resides near the top of the image. The star system, about 120 times more massive than the Sun, produced a spectacular outburst that was seen on Earth from 1837 to 1858. But some of the light from the eruption took an indirect path and is just now reaching our planet. The light bounced off dust clouds (the boxed region at the bottom of the image, indicating an area of space that lies about 100 light-years away ) and was rerouted to Earth, a phenomenon called a light echo. The image was taken in February 2000 by the U.S. National Optical Astronomy Observatory's Curtis Schmidt Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. The three black-and-white images at right show light from the eruption illuminating dust clouds near the doomed star system as it moves through them. The effect is like shining a flashlight on different regions of a vast cavern. The images were taken over an eight-year span by the U.S. National Optical Astronomy Observatory's Blanco 4-meter telescope at the CTIO. Credit: NASA, NOAO, and A. Rest (Space Telescope Science Institute, Baltimore, Md.)

Eta Car (the LBV) is a massive dying star.  Such stars do not make up the majority of stellar systems in our galaxy, so of course, astronomers are quite interested in what sort of death process Eta Car will go through. Unlike our Sun, which will sort of gently swell to become a red giant (and lose much of its mass in a less-explosive manner), Eta Car will likely go out in a huge cataclysm called a supernova.  Some astronomers suggest it could be such a catastrophic event it would be termed a “hypernova.”

However it blows, Eta Car’s passing will afford astronomers with a ringside seat to stellar mass destruction. The first thing they’ll detect when it blows is a gamma-ray burst that could affect our communications satellites.  After that, they’ll be busy cataloguing the process of the explosion and the ring of debris that will be rushing out to space.  Some astronomers have suggested that this explosion could happen anytime from the next few years to a few million years from now.  Regardless of when it blows, it’s not likely to hurt us much on Earth, since the rotational axis of the system is pointed away from us.

Hubble Space Telescope has been observing Eta Car for a couple of decades now, watching subtle changes in the cloud surrounding the stellar pair, and analyzing the mixes of gas and dust in that cloud. The most recent observations actually pinpoint an echo of the light from the Great Eruption bouncing off more distant parts of the clouds.   The observations of the light echoes mark the first time astronomers have used spectroscopy to analyze a light echo from a star undergoing powerful recurring eruptions, though they have measured this unique phenomenon around exploding stars called supernovae. In spectroscopy, light from an object is captured by the telescope and sent to an instrument (called a spectrograph) that breaks that light into all its wavelengths. Each wavelength of light tells you something about the chemical makeup of the object, its speed through space, whether or not it is spinning, and gives a measure of its temperature.  For the Hubble observations, the spectrograph  captured Eta Car’s characteristic “fingerprints,” providing details about its behavior, including the temperature and speed of the ejected material.

The light echoes from Eta Car are telling astronomers that this restless, heaving old star system does not behave like other stars of its class.  The temperature of the outflow from Eta Carinae’s central region, for example, is about 8,500 degrees Fahrenheit (5,000 Kelvin), which is much cooler than that of other erupting stars. So,this gives some important clues about what’s happening inside the star.  There are other clues in the stream of light HST is studying, and light from the outburst is still on its way to Earth. Astronomers are expecting another brightening in about six months and that will give them more data to chew on as they seek to understand how this star is going through its death process. So, stay tuned.  There’s more news on the way from Eta Car!





Black Holes, Stars, Planets, Galaxies, and the Cosmos



February 15, 2012 at 11:41 am | Leave a Comment

That’s What I Write About

I’ve been running this blog since just after the Cosmic Dark Ages ended (about the time blogs began), and in it, I write about astronomy and space topics.  If you analyze what I’ve written about over the years, you’ll see that I like to write about Mars or black holes, or colliding galaxies, or other such fascinating topics.  They are part and parcel of understanding the origin and evolution of everything in the universe.

Black holes are objects that were once just an idea in a scientist’s brain, but as more and more observations of strange objects came through our telescopes, and as we were able to apply the laws of physics, motion, and gravity to explain these observations, our understanding of black holes grew. Today, we find them all over the place — they’re not new objects, but our discovery and understanding of them is relatively new (in the grand scheme of things, as one of my astronomy professors used to say).

Stars are all over the place.  The closest one is the Sun, and that’s the one that we based our understanding of other stars — and their formation, evolution, and deaths — upon. Of course, nowadays, we study many different types of stars, and know that the formation is roughly the same for all stars. The evolution is similar, up to a point. The deaths, however, are wildly different, depending on the mass of the star.  So, a star like the Sun forms in a cloud of gas and dust, just as every other star does.  It consumes nuclear fuel in its core and in return, puts out light and heat.  Most stars do that. But,when the Sun dies, it will go quietly — in comparison to a star with several tens of solar masses or larger. Those massive stars will explode as supernovae.  Big difference.

In dying, all stars lose mass to the cosmos. That mass, in the form of gas and dust, enriches the interstellar medium, and from that “enrichment” we get the materials from which other stars — and planets (and comets, asteroids, rings, moons) are made.  Planets are the ashes of dead stars… as are we, since we evolved on a planet, and our bodies contain the same materials.

All stars and planets are part of galaxies, which are huge conglomerations of stars and varying amounts of interstellar material.  Galaxies first formed a few hundred million years after the universe began, and they have formed and reformed, collided, reshaped themselves into larger galaxies, ever since.

These are the objects (and some of the processes) that I like to write about in this blog. Occasionally, I will stray into other topics, such as politics, or how you can view the sky, and that’s fine.  As long as the subject is somehow related to astronomy, planetary science, space science — you get the idea — I write about it. It’s my blog, my rules. And, it’s my way of sharing (for free) the topics I learned about in graduate school with people who are also interested in those topics.

I don’t get a lot of comments from people who want to talk about those sciences. When I do, I allow them to be posted (I moderate comments).  Mostly, though, I weed out crap from the comment feed.  Most of the comments that get posted are not related to the subject, or they’re spam.  Luckily, I moderate comments, and I have a good spam filter. So, all those half-literate, fake English spam comments that tell me that the writer is part of a collective that wants to start blogging and will I help, or tell me that my blog looks weird in some browser I’ve never heard of, or that post gibberish with a link to a pr0n site — those bots are wasting the sender’s time and money. They don’t get posted here.

What do I NOT write about?  It’s easier to say what this blog isn’t. It’s NOT a public relations device.  It’s not an instant “news” service where someone can send me a story and I’ll publish it unread. And, it’s not a place where they can send some fluffy press release that has nothing to do with the topics I DO write about and expect me to give free publicity. Same goes with half-baked, illogical conspiracy theories that the senders want me to use to “expose” the government, the Trilateral Commission, NASA, the medical profession, big pharma, big Farma, the Greys, the Pleiadeians, etc. etc.

Not gonna happen.  I make a living as a writer talking about scientific exploration; so folks who expect me to be their free publicity machine should consider respecting my expertise and interests, rather than expecting a free ride.

I DO happily accept press releases each day from vetted sources that talk about recent discoveries in astronomy, space science, planetary science, astrobiology, related technologies, legitimate cosmology, and so forth.  And, I use that information to do more research into the topics they discuss, and then create stories that share the cosmos (and our exploration of it) with my readers.

All that stuff I DO like to write about is the stuff of the cosmos. It teaches the wonders of the universe. It’s science at its purest, hardest, and most satisfying. What could be better than that?





Mars and the Search for Water



February 7, 2012 at 21:09 pm | Leave a Comment

Mars Express Radars Mars

New results from the MARSIS radar on Mars Express give strong evidence for a former ocean of Mars (marked in blue on this artist's concept of what early Mars may have looked like when this ocean existed). The radar detected sediments reminiscent of an ocean floor inside previously identified, ancient shorelines on the red planet. The ocean would have covered the northern plains billions of years ago. Credits: ESA, C. Carreau

It’s one of those no-brainer ideas: that water once existed on the surface of Mars.  All you have to do is LOOK at the planet and you see evidence of something that flowed across the surface.  There are washed out valleys, what look like river canyons, and regions that look like the shores of ancient oceans. If we had geologists (areologists?) on the planet, they’d make short work of determining what it was that flowed across the planet’s surface by taking surface samples and analyzing them.

Well, we don’t have people on Mars — yet. But, we do have spacecraft orbiting the planet and sitting on its surface sending us back all manner of daily data about this rusty, red desert world. The European Space Agency’s Mars Express mission has a radar instrument called MARSIS that bounced signals from the surface back to its detectors. The data in those signals told planetary scientists that at least one part of Mars is covered with sediments that were probably laid down on the floor of an ancient ocean.  The sediments contain minerals and possibly some ices that identify the area as the site of an ocean that existed perhaps 3 or 4 billion years ago, when Mars was very young, and possibly warmer and wetter than what we see today.

The oceans probably didn’t last very long; their water frozen into place, or vaporized and escaped through the planet’s thin atmosphere to space. So, the chances for life to form in those oceans were likely pretty thin.  Life or no life, the evidence for water flowing on the Martian surface in the dim recesses of history is pretty exciting. Now, the questions remain: where did all the water go and was there ever a chance that Mars harbored life?  Stay tuned!

Speaking of staying tuned, have you checked in on this month’s “Our Night Sky” at Astrocast.TV?  If not, why not?  Learn what’s up in the February skies!  You might find Mars…





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Image of Horsehead Nebula: T.A.Rector (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA)

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