The Sun as viewed by the Solar and Heliospheric Observatory (NASA/SOHO)
Think you know everything there is to know about the Sun? Think again. Here are 10 facts about the Sun, collected in no particular order. Some you might already know, and others will be totally new to you.
1. The Sun is the Solar System
We live on the planet, so we think it’s an equal member of the Solar System. But that couldn’t be further from the truth. The reality is that the mass of the Sun accounts for 99.8% of the mass of the Solar System. And most of that final 0.2% comes from Jupiter. So the mass of the Earth is a fraction of a fraction of the mass of the Solar System. Really, we barely exist.
2. And the Sun is mostly hydrogen and helium
If you could take apart the Sun and pile up its different elements, you’d find that 74% of its mass comes from hydrogen. with 24% helium. The remaining 2% is includes trace amounts of iron, nickel, oxygen, and all the other elements we have in the Solar System. In other words, the Solar System is mostly made of hydrogen.
3. The Sun is pretty bright.
We know of some amazingly large and bright stars, like Eta Carina and Betelgeuse. But they’re incredibly far away. Our own Sun is a relatively bright star. If you could take the 50 closest stars within 17 light-years of the Earth, the Sun would be the 4th brightest star in absolute terms. Not bad at all.
4. The Sun is huge, but tiny
With a diameter of 109 times the size the Earth, the Sun makes a really big sphere. You could fit 1.3 million Earths inside the Sun. Or you could flatten out 11,990 Earths to cover the surface of the Sun. That’s big, but there are some much bigger stars out there. For example, the biggest star that we know of would almost reach Saturn if it were placed inside the Solar System.
5. The Sun is middle aged
Astronomers think that the Sun (and the planets) formed from the solar nebula about 4.59 billion years ago. The Sun is in the main sequence stage right now, slowly using up its hydrogen fuel. But at some point, in about 5 billion years from now, the Sun will enter the red giant phase, where it swells up to consume the inner planets – including Earth (probably). It will slough off its outer layers, and then shrink back down to a relatively tiny white dwarf.
6. The Sun has layers
The Sun looks like a burning ball of fire, but it actually has an internal structure. The visible surface we can see is called the photosphere, and heats up to a temperature of about 6,000 degrees Kelvin. Beneath that is the convective zone, where heat moves slowly from the inner Sun to the surface, and cooled material falls back down in columns. This region starts at 70% of the radius of the Sun. Beneath the convection zone is the radiative zone. In this zone, heat can only travel through radiation. The core of the Sun extends from the center of the Sun to a distance of 0.2 solar radii. This is where temperatures reach 13.6 million degrees Kelvin, and molecules of hydrogen are fused into helium.
7. The Sun is heating up, and will kill all life on Earth
It feels like the Sun has been around forever, unchanging, but that’s not true. The Sun is actually slowly heating up. It’s becoming 10% more luminous every billion years. In fact, within just a billion years, the heat from the Sun will be so intense that liquid water won’t exist on the surface of the Earth. Life on Earth as we know it will be gone forever. Bacteria might still live on underground, but the surface of the planet will be scorched and uninhabited. It’ll take another 7 billion years for the Sun to reach its red giant phase before it actually expands to the point that it engulfs the Earth and destroys the entire planet.
8. Different parts of the Sun rotate at different speeds
Unlike the planets, the Sun is great big sphere of hydrogen gas. Because of this, different parts of the Sun rotate at different speeds. You can see how fast the surface is rotating by tracking the movement of sunspots across the surface. Regions at the equator take 25 days to complete one rotation, while features at the poles can take 36 days. And the inside of the Sun seems to take about 27 days.
9. The outer atmosphere is hotter than the surface
The surface of the Sun reaches temperatures of 6,000 Kelvin. But this is actually much less than the Sun’s atmosphere. Above the surface of the Sun is a region of the atmosphere called the chromosphere, where temperatures can reach 100,000 K. But that’s nothing. There’s an even more distant region called the corona, which extends to a volume even larger than the Sun itself. Temperatures in the corona can reach 1 million K.
10. There are spacecraft observing the Sun right now.
The most famous spacecraft sent to observe the Sun is the Solar and Heliospheric Observatory, built by NASA and ESA, and launched in December, 1995. SOHO has been continuously observing the Sun since then, and sent back countless images. A more recent mission is NASA’s STEREO spacecraft. This was actually two spacecraft, launched in October 2006. These twin spacecraft were designed to watch the same activity on the Sun from two different vantage points, to give a 3-D perspective of the Sun’s activity, and allow astronomers to better predict space weather.
ESA Astronaut Frank DeWinne on board the ISS. Credit: ESA
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The European Space Agency needs a bang-up, attention-grabbing moniker for the next long duration European mission to the International Space Station, and they are holding a competition for the public to submit a suitable name. In May 2009, ESA astronaut Frank De Winne, of Belgium will fly to the ISS for a six month mission. ESA is holding a competition to find a name for the mission. Have any great ideas? Here are the parameters for the competition:
The name has to reflect the following aspects:
1. Europe is exploring space, and humans are explorers by nature. Europe has a legacy in exploring Earth and will live up to the expectations in exploring Space.
2. Europe has its own Columbus laboratory permanently in space on the ISS. Europe uses its Columbus laboratory on the ISS for science, technology and education for the benefit of life on Earth.
3. From space our planet looks blue because of the water. Water is the basis of life; Clean water is the basis for healthy life of all humans on Earth.
Wow, that’s a tough set of parameters. Now, here’s a few rules: (for the full rules see HERE)
1. The competition is open to all citizens of the ESA Member States (sorry US and Canada folks, you’re out of luck on this one.)
2. The proposals have to arrive in the [email protected] mailbox the latest by 18:00 CEST, 15 October 2008.
3. The proposal should be maximum of one page, with 12 pt single spacing
4. The name should be a word (or a short combination of words), not a personal name (unless it is a mythological name which has a commonly known symbolic meaning).
Again, here’s the full rules. Have fun and go for it!
Team members gather to inspect and collect a meteorite being placed in a Teflon bag. Photo credit: M. Keiding, 2007
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Antarctica’s distinctive, unforgiving environment is truly unique. But add to that setting the otherworldly task of looking for meteorites — bits and pieces from the far reaches of our solar system that are strewn about Antarctica’s icy surface,– and Earth’s southern-most continent can provide a truly unparalleled scientific experience. “I had the privilege to explore a part of the world that few people get to,” said Dr. Lucy McFadden, a research professor in the astronomy department at the University of Maryland, College Park. She also is a scientist in the education and public outreach area for NASA’s Dawn mission that is traveling to study the asteroids Ceres and Vesta. McFadden had the opportunity to travel to Antarctica and spend over six weeks hunting for meteorites, specifically looking for meteorites from Ceres and Vesta. She shared her experiences recently in an online “webinar,” answering questions about her journey. “I love sharing my adventures,” she said. “My excitement about exploring the solar system was renewed because I had the opportunity to explore Earth as a planet.”
Although meteorites fall uniformly all over the Earth –estimates are between 30-80 tons a year, — most are in the form of dust. For the bigger rock-sized pieces, many fall in the ocean and those that fall on land can be buried by shifting terrain, broken down by chemical weathering, or are easily confused with Earth rocks. But Antarctica’s blue ice sheets are clear and barren, making it easy to spy a dark rock that’s likely a sample from space.
Aerial view of Antarctica. Photo credit: L. McFadden 2008
However, there’s another reason Antarctica is such a great place to look for meteorites. “There’s something special about Antarctica. Meteorites collect in certain areas there,” McFadden said. “The ice sheets are always moving, and the meteorites move with them. But the rocks get trapped by the barriers of the mountains, and that’s where the meteorites are found. Once you get a meteorite up against a barrier, the constant blowing of the polar winds ablates the ice, and rocks effectively come to the surface.” Over periods of tens or hundreds of thousands of years, very significant concentrations can build up in these areas.
Since 1976, the U.S. National Science Foundation has supported an annual search for meteorites during the Antarctic summer, through a program called ANSMET, the Antarctic Search for Meteorites. McFadden was part of an eight-member meteorite hunting team in November 2007 to January 2008.
McMurdo Station. Photo credit: L. McFadden, 2008
A C-17 cargo plane brought the team to Antarctica’s McMurdo Station. But one doesn’t just go out and start hunting for rocks without instructions on how to survive Antarctica’s harsh environment. The team underwent a week of training that included lessons on proper clothing. “I had to learn which coat to put on when, which hat and gloves to wear and be sure to have my boots on,” said McFadden. “It brought me back to kindergarten.” Also, learning snowmobile operation and repair is a must, as that would be their mode of transportation during their expeditions. “We were trained how to stay away from the crevasses in the ice and trained for rescue in case someone fell in,” she said.
A plane then brought the team, the snowmobiles, fuel and gear to their field site on the Miller Range to set up camp. They erected tents – their homes for six weeks, and had to chip ice to get water for drinking and cooking. Typical daytime temperature was about 20 degrees Fahrenheit (-6 C) when there wasn’t a storm. High winds at field camp. Photo credit: L. McFadden, 2007
At 70 degrees south latitude, the Antarctic summer sun never set. But the surroundings were desolate, to say the least. The region is mountainous, but constantly snow and ice covered. “I felt a sense of vulnerability of us humans,” McFadden said. “This is not a hospitable environment.” She also worried about the possibility of getting lost in the barren landscape with few landmarks. But with them was a seasoned, expert guide, John Schutt.
So what’s the trick of finding meteorites in Antarctica? “We practiced around the camp first, and walked up to all the rocks in the area,” said McFadden. “There are other rocks on the ground from rockslides from the mountains, so you have to learn what the local rocks look like.” Dr. Ralph Harvey, the head of the ANSMET program taught the team the art of meteorite hunting.
“When you find a field of rocks, you have to look closely and separate out the regular rocks from meteorites,” McFadden said. Most meteorites are black because they have a fusion crust: a thin glassy rind that forms on meteorites when they are coming through the atmosphere. The friction heats them up and the outside of the meteorite melts just a little.
“We looked at each rock,” said McFadden. “If we thought we found a meteorite, we waved our arms and everyone would come over and look. If we determined it was a meteorite, we would pick it up with tongs and put it in a Teflon bag and mark it. Then we planted a flag where we found a meteorite. It was very satisfying to look back where we’d been and see all the flags.”
Flags marking meteorite finds. credit: M. Keiding and ANSMET 2007-2008.
They followed a certain procedure to make notes on each meteorite, take pictures, note the position of each sample with a Global Positioning System monitor, and then wrap the meteorites in a certain way and put them in backpacks. “It was a big process to catalogue and account for all of them,” McFadden said.
At the end of the day they collected all the rocks from the backpacks and put them in bags in a specialized container to keep them cold. This would avoid contamination from any snow that might be attached to the rocks, until they are brought to Johnson Space Center where they are catalogued and then distributed to scientists around the world. A large meteorite found by the team. Photo credit: ANSMET 2007 Case Western Reserve University
Each of the meteorites tells a story about the processes of the early solar system. Scientists who study meteorites can find clues to the conditions as our solar system evolved, and find out more about the asteroids, moons and planets the meteorites originate from. Meteorites represent a “free” sample return mission for scientists.
The team didn’t do any scientific analysis out in the field, just collected the samples for transport to the laboratories in Houston. But that doesn’t mean they didn’t examine the rocks!
The team found lots of carbonaceous chondrites with very irregular and jagged shapes, some that may have come from the Moon, and others with a green mineral called olivine that may have come from Mars. One meteorite found made the team think of the famous ALH 84001 meteorite found in the Allan Hills region of Antarctica, that made headlines in 1996 when it was announced that the meteorite may contain evidence for traces of life from Mars. “We wondered if this one meteorite was related to ALH 84001,” said McFadden. But the team won’t know the answer until geochemical analyses are performed.
As for her search for samples from Ceres and Vesta, McFadden said, “I think we might have been successful in finding samples from Vesta, but I was really interested in looking for samples from Ceres. However, I wasn’t really sure what I was looking for. As far as we know we don’t have samples from Ceres.” Small meteorite. Photo credit: ANSMET 2007 Case Western Reserve University
How do scientists know a meteorite came from a specific asteroid? “The whole study of meteoritics addresses that through laboratory studies of many different attributes of rocks,” said McFadden. “We know we have rocks in our meteorite collection from Vesta because about one in every seven meteorites we find has characteristics, or spectral signature, that matches Vesta as viewed through a telescope. We look at Vesta and see a huge impact basin that the meteorites probably came from.”
But Ceres is a different matter. “We don’t know much about Ceres,” she said. “The spectral signature of Ceres doesn’t match anything we have in the meteorite collection. But maybe they’ll find one in the samples we brought back or eventually find one on a future expedition.”
Snowmobiles, the vehicle of choice for Antarctic meteorite hunting. Photo credit: L. McFadden, 2007
With stormy periods when they had to huddle in their tents, McFadden’s team had 22 full days of meteorite searching, and eight half days. They went out at 9:00 am, returning at 5:00 pm. “We had six guys and two women,” said McFadden. It’s different for each expedition. We didn’t know each other before hand, but we worked well together. We had this common experience and we had to look out for each other. But it was also very lonely; there wasn’t that much opportunity to interact. We were exhausted each night.”
They did have opportunities for recreation such as skiing, playing games or reading books. One particularly nice day they made a couch from snow and sat outside for awhile. Planes occasionally brought re-supply of food, letters, and other supplies. They were in Antarctica for Christmas, so they decorated and had a potluck supper. “The isolation and cold weather got to us after awhile, but we loved our time out there,” McFadden said. “We looked forward to going home, but we had a tremendous experience. We all appreciated the beauty of Antarctica.” Aerial view near McFadden's field camp in the Miller Range. Photo credit: M. Keiding, 2007
Their expedition found 710 meteorites, some as small as a little finger nail (about 1.0 x 0.5 x 0.5 cm) 3a), and others about 8 pounds and too big to hold in one hand (about 25 cm x 15 cm x 12).
“We had good hunting,” she said. “It wasn’t a record. Some days we wanted to keep going, but our guide had to keep us in check and keep us safe. In that climate you do have to stop and take care of yourself.”
Over the more than 25 years of these expeditions, over 26,000 meteorites have been found, expanding the volume of extraterrestrial materials that can be studied here on Earth to provide a context for our remote sensing explorations out in the solar system, such as the Dawn mission. “My experience searching for meteorites inspired me to continue trying to understand the meteorites themselves and pair that with my exploration with the Dawn spacecraft that is searching out in the solar system,” said McFadden.
And now another team of scientists is preparing to return to Antarctica in November this year to continue the hunt.
Dr. Lucy McFadden, Dawn Co-Investigator and Education and Public Outreach (E/PO) lead Photo credit: M. Keiding, 2007
McFadden responded to the question of why teams keep going back every year to look for meteorites. “There is the potential to find new types of meteorites. In 2006, they found a type of meteorite that had never been seen before. They believe it’s from another body in our solar system that was probably the size of the moon, but its isotopic signature is decidedly different from the moon or Mars. So we have indeed found evidence of planetesimals that are new to us that are out there in the asteroid belt. That’s very exciting and that keeps us going.”
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This week we have another new host for the Carnival of Space: OrbitalHub. Learn more about the upcoming Hubble servicing mission, the end of shuttle flights in 2010, and why space exploration is justified.
And if you’re interested in looking back, here’s an archive to all the past carnivals of space. If you’ve got a space-related blog, you should really join the carnival. Just email an entry to [email protected], and the next host will link to it. It will help get awareness out there about your writing, help you meet others in the space community – and community is what blogging is all about. And if you really want to help out, let me know if you can be a host, and I’ll schedule you into the calendar.
Finally, if you run a space-related blog, please post a link to the Carnival of Space. Help us get the word out.
Artist concept of a fission surface power system on the surface of the moon. Credit: NASA
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When astronauts return to the moon for long duration missions, they will need reliable sources of power. Solar energy will be plentiful for the 14 Earth-day- long lunar daytime, but what about the equally as long lunar night? NASA engineers are exploring the possibility of nuclear fission to provide the necessary power. If you’re having visions of a Three Mile Island nuclear reactor on the moon, put your fears to rest. A nuclear reactor used in space is much different than Earth-based systems, says Lee Mason of the NASA Glenn Research Center, who is the principal investigator for testing a fission powered system for the moon. There are no large concrete cooling towers, and the reactor is about the size of an office trash can. Of course, it won’t produce as much energy as the big reactors on Earth, but it should be more than adequate for the projected power needs of a lunar outpost.
“Our goal is to build a technology demonstration unit with all the major components of a fission surface power system and conduct non-nuclear, integrated system testing in a ground-based space simulation facility,” said Mason. “Our long-term goal is to demonstrate technical readiness early in the next decade, when NASA is expected to decide on the type of power system to be used on the lunar surface.”
A fission surface power system on the moon has the potential to generate a steady 40 kilowatts of electric power, enough for about eight houses on Earth. It works by splitting uranium atoms in a reactor to generate heat that then is converted into electric power. The fission surface power system can produce large amounts of power in harsh environments, like those on the surface of the moon or Mars, because it does not rely on sunlight. The primary components of fission surface power systems are a heat source, power conversion, heat rejection and power conditioning, and distribution.
Glenn recently contracted for the design and analysis of two different types of advanced power conversion units as an early step in the development of a full system-level technology demonstration. These power conversion units are necessary to process the heat produced by the nuclear reactor and efficiently convert it to electrical power.
Two different companies have designed concepts that can produce a total of 12 kilowatts of power. One uses piston engines and the other a high speed turbine coupled with a rotary alternator.
“Development and testing of the power conversion unit will be a key factor in demonstrating the readiness of fission surface power technology and provide NASA with viable and cost-effective options for nuclear power on the moon and Mars,” said Don Palac, manager of Glenn’s Fission Surface Power Project.
A contractor will be selected after a year of design and analysis. Testing of the non-nuclear system is expected to take place in 2012 or 2013 to verify the performance and safety of the systems and determine if these systems can easily be used on the moon, or even on Mars.
While the Anglo-Australian Telescope is far from being the world’s largest, or even located in the world’s best observing site, it’s still the world’s most productive in terms of astronomy research. According to recently released productivity ratings, the number of scientific papers resulting from observations made with the AAOmega fibre-fed optical spectrograph, SPIRAL Integral Field Unit, IRIS2, University College London Echelle Spectrograph (UCLES), or Ultra High Resolution Facility (UHRF) made the AAT the number one ranked 4-metre-class telescope in the world for more than two years between 2001 and 2003. But what’s going on today is even more important…
When we think of research telescopes, some of the world’s top rated are the Hubble Space Telescope (located in Earth orbit), Keck (more than twice the AAT’s size) in Hawaii, the Very Large Telescope (VLT, which comprises four telescopes twice the size of the AAT) in Chile, the Sloan Digital Sky Survey and the 2MASS telescope. So where does that leave the humble Anglo-Australian? Try number five. “The AAT has a remarkable track record of scientific productivity and impact,” says Prof. Matthew Colless, Director of the Anglo-Australian Observatory. “This is an extraordinary achievement.”
When the Anglo-Australian Observatory opened for business in the early 1970’s, the 4 meter telescope was the standard by which all others were judged. Since that time, research telescope aperture has more than doubled and while the AAT can’t compete in some respects, it has advantages that give it an edge for research. While it isn’t Mauna Kea, Australia still offers up some of the best skies to study our Galaxy and other nearby galaxies and the ability to undertake long-term observations and programs that just won’t work with other observatories. Add to that some very unique instrumentation such as Echidna – a fibre positioner for FMOS, UKidna – A multi-fibre positioner for the UKST, OZPOZ – a fibre positioner for ESO and part of FLAMES, DAZLE – The Dark Age z (redshift) Lyman-alpha Explorer, MOMFOS – Multi-Object Multi-Fibre Optical Spectrograph, ODC – Optical Detector Controllers and AAOmega – next generation optical spectrograph for the AAT and you have a recipe for research. This explains why demand for the telescope remains strong, with 2.5 times as many applications for telescope time as can actually be handled. “The AAO believes that the AAT can maintain this high level of productivity and impact for another decade.” says Prof. Colless.
Over a period of time, the the AAO has produced some of the most inspiring astronomy images ever seen – those taken by David Malin. These are the most extraordinary wide-field astrophotographs made with professional telescopes anywhere and every effort has been made to capture the true colours of distant stars, galaxies and nebulae using innovative photographic techniques and CCD detectors. The images have detailed captions and the full NGC 2000.0 catalogue entry. Galaxy images also carry NASA/IPAC Extragalactic Database (NED) data links. They are a standard of astronomers everywhere. But, progress hasn’t stopped. The AAT’s prime focus has recently been upgraded to accommodate a new generation of highly sensitive CCD detectors. The first colour images made with the new facility are now available, currently only in digital form. Most of the photographic images have recently been digitally re-mastered from the original 3-colour separations. This has allowed the AAO to create new, high resolution versions of many existing images and some new pictures that could not be made photographically.
Just this year a “uniquely ambitious, far-sighted†project won an Australian and UK astronomy team the first Group Achievement Award from the UK’s Royal Astronomical Society. Led by Professor Matthew Colless (Anglo-Australian Observatory) in Australia and Professor John Peacock (University of Edinburgh) in the UK, the thirty-three-member team spent ten years mapping the distribution in space of 220,000 galaxies using the 3.9-m Anglo-Australian Telescope (AAT) in New South Wales — a project called the 2-degree Field Galaxy Redshift Survey (2dFGRS). “The scale of this project made it ground-breaking,†said Matthew Colless. “For the first time we were able to map the positions of a huge number of galaxies and see the subtle effects that reveal the different types of matter in the universe.â€
What was needed was for the area of sky surveyed to be much bigger than, rather than the same size as, the “walls†and “strings†of galaxies being detected. Almost ten times larger than any previous survey, the 2dFGRS was the first study to meet this crucial condition. The survey measured patterns in the distribution of galaxies, on scales from 100 million to 1 billion light-years. Two wedge-shaped pieces of sky were surveyed, so when the galaxies within them were mapped out, the result looked like a bow-tie cut from a sponge: a network of voids and dense regions. The size of the 2dF Galaxy Redshift Survey was made possible only by technological advances developed at the Anglo-Australian Observatory (AAO). The 2dF spectrograph used robotic technology to place optical fibres onto the telescope’s focal plane, where each fibre could collect the light from a single galaxy. By using up to 400 optical fibres, this system allowed the light from up to 400 galaxies to be captured simultaneously.
And the AAT is ensuring that it doesn’t fall behind the times with future technological advancement either….
“We are currently investing $4 million in refurbishing the telescope to ensure that it can operate reliably and efficiently for another ten years, and more than $6 million in a major new instrument, the 400-fibre HERMES high-resolution Spectrograph,” says Prof. Colless. “The primary science drivers for HERMES are ‘Galactic archaeology’ surveys to uncover the formation history of the Milky Way,’ he adds. ‘Extragalactic surveys using the AAOmega instrument and galactic surveys using HERMES will be the flagship science carried out on the AAT over the next 5-10 years. AAOmega and HERMES, and other upgrades to existing instruments, will provide astronomers with powerful tools that will enable them to do competitive, high-impact research using the AAT throughout the coming decade.”
Well, I’ve just been accepted into an elite club of people with astronomical objects named after them. And no, my Mom didn’t name a star after me. The asteroid hunting team of David Healy and Jeff Medkeff have collectively discovered 487 asteroids, and designated 62 of them. You might already recognize some of asteroid names: Philplait, Paulmyers, Rebeccawatson, and Derekcolanduno.
At the end of August I received an email from David Healy notifying me that I was a new member of the asteroid club.
Asteroid 158092 Frasercain was officially designated on August 21, 2008. You can see the full list of named asteroids here – scroll down to see Frasercain. And you can see its current position in the Solar System here.
Those of you who know Jeff Medkeff will know the sad part of this story. Jeff, aka “The Blue Collar Scientist”, passed away on August 3rd from complications with liver cancer – he was 39. I’ve got to be honest and tell you that I didn’t know Jeff. We clearly ran in similar circles, but it wasn’t until Phil, Pamela and other people in the space blogging community informed me of his death that I found and read through his blog; I really wish I’d found it earlier.
It’s Wednesday, so that means its time for another “Where In The Universe” (WITU) challenge to test your visual knowledge of the cosmos. This one might be relatively easy, but I’m feeling generous today. Guess what this image is, and give yourself extra points if you can guess which spacecraft is responsible for the image. As always, don’t peek below before you make your guess. Comments on how you did are welcome.
Ready? Go!
This is the Eskimo Nebula (NGC 2392), so named because it resembles a person’s head surrounded by a parka hood. But its also known as the Clownface Nebula. In 2000, the Hubble Space Telescope produced this image. NGC 2392 lies about 3000 light-years away and is visible with a small telescope, found in the constellation of Gemini.
The gas clouds in this nebula are unusual and complex, and aren’t fully understood. Its a planetary nebula, and the gas seen above composed the outer layers of a Sun-like star only 10,000 years ago. The inner filaments visible above are being ejected by strong wind of particles from the central star. The outer disk contains unusual light-year long orange filaments.
Eta Carinae Credit: Gemini Observatory artwork by Lynette Cook
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There’s ‘smoked but didn’t inhale,’ ‘promised but didn’t deliver,’ and now there’s ‘exploded but didn’t destroy.’ Eta Carinae, the galaxy’s biggest, brightest and perhaps most studied star after the sun, appears to be driven by an entirely new type of stellar explosion that is fainter than a typical supernova and does not destroy the star. Astronomer Nathan Smith proposes that Eta Carinae’s historic 1843 explosion was, in fact, an outburst that produced a fast blast wave similar to, but less energetic than, a real supernova. This well-documented event in our own Milky Way Galaxy is probably related to a class of faint stellar explosions in other galaxies recognized in recent years by telescopes searching for extragalactic supernovae.
“There is a class of stellar explosions going off in other galaxies for which we still don’t know the cause, but Eta Carinae is the prototype,” said Smith, a UC Berkeley postdoctoral fellow.
Eta Carinae (η Car) is a massive, hot, variable star visible only from the Southern Hemisphere, and is located about 7,500 light years from Earth in a young region of star birth called the Carina Nebula. In 1843, observers saw Eta Car brighten immensely. Visible now is the resulting cloud of gas and dust, known as the Homunculus nebula, wafting away from the star. A faint shell of debris from an earlier explosion is also visible, probably dating from around 1,000 years ago.
But these shells of gas and dust are moving relatively slowly at 650 kilometers per second (1.5 million miles per hour) compared to the blast shell of a regular supernova.
Presumably blown off by the star’s fierce wind, the shells of gas and dust are moving slowly – at speeds of 650 kilometers per second (1.5 million miles per hour) or less – compared to the blast shell of a supernova. But new observations by Smith show filaments of gas moving five times faster than the debris from the Homonuculus, which would equal speeds of materials accelerated fast blast wave of a supernova explosion.
The fast speeds in this blast wave could roughly double earlier estimates of the energy released in the 1843 eruption of Eta Carinae, an event that Smith argues was not just a gentle surface eruption driven by the stellar wind, but an actual explosion deep in the star that sent debris hurtling into interstellar space. In fact, the fast-moving blast wave is now colliding with the slow-moving cloud from the 1,000-year-old eruption and generating X-rays that have been observed by the orbiting Chandra Observatory.
“These observations force us to modify our interpretation of what happened in the 1843 eruption,” he said. “Rather than a steady wind blowing off the outer layers, it seems to have been an explosion that started deep inside the star and blasted off its outer layers. It takes a new mechanism to cause explosions like this.”
If Smith’s interpretation is correct, supermassive stars like Eta Carinae may blow off large amounts of mass in periodic explosions as they approach the end of their lives before a final, cataclysmic supernova blows the star to smithereens and leaves behind a black hole.
“Looking at other galaxies, astronomers have seen stars like Eta Carinae that get brighter, but not quite as bright as a real supernova,” he said. “We don’t know what they are. It’s an enduring mystery as to what can brighten a star that much without destroying it completely.”
After a quick Dragon*Con break, we’re back to our tour through the fundamental forces of the Universe. We’ve covered gravity and electromagnetism, and now we’re moving onto the strong and weak nuclear forces. We didn’t think they’d really need to be separate episodes, so we’re putting them together. And then we’ll cap the whole series with the quest for the theory of everything.
