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Goodsell Observatory, Carleton College MN

The Carina Nebula: Star Birth in the Extreme

Also known as the Great Nebula in Carina, or NGC 3372, the Carina Nebula is a large, bright nebula that surounds several open clusters of stars - such as Eta Carinae and HD 93129A, two of the most massive and luminous stars in the Milky Way galaxy. Carina is  between 6,500 and 10,000 light years from Earth. It appears in the constellation of Carina, and is located in the Carina–Sagittarius Arm. 

The Carina Nebula was discovered in 1751-1752 by Nicolas Louis de Lacaille in 1751–52 from the Cape of Good Hope. The nebula is one of the largest diffuse nebulae in our skies. Although it is some four times as large and even brighter than the famous Orion Nebula, the Carina Nebula is much less well known, due to its location far in the Southern Hemisphere. 

Stars Enrich the Universe

One of the most widely known and repeated astrophysical facts is that stars produce all the heavy elements that eventually make planets, shrubberies, and the likes of us. It’s absolutely true, but how exactly do they get those elements out into the universe to do all that?

A major route is stellar explosion. When supernovae go off they spew element-rich matter into the cosmos on a big scale, pushing it out for as much as a few hundred light years. But it’s not the only way for a star to dig into its pockets to hand out loose change. In fact, all moderately massive stars – from roughly solar mass to several times larger – can go through a phase after they’ve exhausted the fusion of hydrogen in their cores where they expel huge amounts of material. They do this by periodically inflating their outskirts, and then blowing this matter out to interstellar space. As much as half the mass of the star can be cast off this way. This freshly produced star-stuff consists of both gas and microscopic dust grains that are produced as the gas cools down away from the star and quite literally condenses out, forming silicate or carbon particles (the latter from lower mass stars). This hazy outflow dumps new elements into space to produce some beautiful structures, known rather confusingly as ‘planetary’ nebula.

The Cat’s Eye Nebula - matter blown from a star (NASA, ESA, HEIC, and The Hubble Heritage Team (STScI/AURA))

The Ring Nebula (The Hubble Heritage Team (AURA/STScI/NASA))

The problem is that we haven’t fully understood how stars perform this trick. The only tool they have at their disposal is the pressure of stellar photons – light flooding from the star can push and accelerate material away from it. However, getting this light to push against the gas of the stellar atmosphere efficiently enough to set it in motion has seemed difficult. One option is that the tiny grains of dust act like miniature solar sails, that in turn snowplough through the gas to accelerate it along in front of them. However this theory has had some gaps in it; figuring out the necessary combination of dust grain composition, size, and location of formation has been tricky.

A new investigation recently published by Norris et al. in the journal Nature (and discussed in an excellent companion piece by Susanne Höfner) exploits some very clever astronomical observations of flatulent old stars to find a possible solution. By studying the polarized light from a number of these systems, and by usinginterferometric techniques, the authors were able to test the properties of dust that appears to be produced remarkably close to stellar surfaces, at barely a couple of stellar radii away.

The dust particles are surprisingly large, with diameters of about 600 nano-meters (0.0006 millimeters), and must be quite transparent to the stellar light or else they would be boiled away as they absorbed radiation. Yet this would seemingly make them poor solar sailors. The solution to this conundrum is that these are silicate grains (perhaps magnesium silicate) that scatter the starlight rather than absorb it, like rather rough mirrors. These ‘big’ grains can be readily pushed outwards at speeds of 20,000 miles an hour, and they will sweep up anything in their way.

Thus, the dispersal of elements into the cosmos may owe a lot to a most peculiar type of sandstorm, taking place in the messiness around dying stars. This remarkable process may be critically important to understand for cosmological reasons as well. Höfner points out that the more massive stars that go through this stage are also the likely progenitors of Type Ia supernovae, the explosions cosmologists use to track the changing expansion rate of the universe. Proper knowledge of the true, sandy environment of these vital yardsticks would be a very good thing.

The Tarantula Nebula

Also known as 30 Doradus or NGC 2070, the Tarantula Nebula is a gorgeous region in the Large Magellanic Cloud (LMC). Although originally thought to be a star, Nicolas Louis de Lacaille proved it to be a nebula in 1751. This brand new picture was recently taken by the Hubble Space Telescope. 

For a non-stellar object, the Tarantula Nebula is extremely luminous - fairly easily seen with an apparent magnitude of 8. In fact, “Its luminosity is so great that if it were as close to Earth as the Orion Nebula, the Tarantula Nebula would cast shadows.” It is located nearly 160,000 light years away - and is the most active starburst region known in the Local Group of galaxies. 

The core of the Tarantula Nebula contains the compact star cluster R136, which produces most of the energy that renders the nebula so easily visible. ]The estimated mass of the cluster is 450,000 solar masses, suggesting it will likely become a globular cluster in the future.

Kepler Mission Extended to 2016

With NASA’s tight budget, there were concerns that some of the agency’s most successful astrophysics missions might not be able to continue. Anxieties were rampant about one mission in particular, the very fruitful exoplanet-hunting Kepler mission, as several years of observations are required in order for Kepler to confirm a repeated orbit as a planet transits its star. But today, after a long awaited Senior Review of nine astrophysics missions, surprisingly all have received funding to continue at least through 2014, with several mission extensions, including Kepler.

“Ad Astra… Kepler mission extended through FY16! We are grateful & ecstatic!” the@NASAKepler Twitter account posted today.

Additionally, missions such as Hubble, Fermi and Swift will receive continued funding. The only mission that took a hit was the Spitzer infrared telescope, which – as of now — will be closed out in 2015, which is sooner than requested.

The Senior Review of missions takes place every two years, with the goal assisting NASA to optimize the scientific productivity of its operating missions during their extended phase. In the Review, missions are ranked as which are most successful; previous Senior Reviews led to the removal of funding for the weakest 10-20% of extended missions, some of which had partial instrument failures or significantly reduced capabilities.

But this year’s review found all the astrophysics mission to be successful.

Here’s a rundown of the missions and how their funding was affected by the Senior Review:

• The Hubble Space Telescope will continue at the currently funded levels.

• Chandra will also continue at current levels, but its Guest Observer budget will actually be increased to account for decreases in Fiscal Year 2011.

• Fermi operations are extended through FY16, with a 10 percent per year reduction starting in FY14.

• Swift and Kepler mission operations are extended through FY16, including funding for data analysis.

• Planck will support one year extended operations of the Low Frequency Instrument (LFI).

• Spitzer’s operations are extended through FY14 with closeout in FY15.

• U.S. science support of Suzaku is extended to March 2015.

• Funding for U.S. support of XMM-Newton is extended through March 2015.

NASA says that all FY15-FY16 decisions are for planning purposes and they will be revisited in the 2014 Senior Review.

How Common is Life in the Milky Way? 

As Captain Kirk and his crew explore the Milky Way (and far, far beyond) they regularly encountering alien life. Often these life forms resemble humans, and frequently they have developed into civilizations far more advanced than those seen on Earth.

Star Trek – I hate to break it to you – is a work of fiction. But while screenwriters have been sending the Starship Enterprise on its voyages to the final frontier, astronomers here on Earth have also been searching for alien worlds. They have been using telescopes to hunt for exoplanets and for signs that life could exist on them, such as whether these planets resemble Earth and whether they orbit within a habitable distance away from their parent stars.

Yesterday, astronomers announced a discovery that could give second-Earth-hunters a reason to be optimistic. Results from the European Southern Observatory’s High Accuracy Radial velocity Planet Searcher (HARPS) instrument revealed that our galaxy could be awash with rocky super-Earths orbiting within the habitable zones around faint red stars. The international team of researchers claims that there may be tens of billions of such planets in the Milky Way alone, and probably about 100 in the Sun’s immediate neighbourhood.

So is this a sign that life more than likely does exist in our galaxy? Or should we interpret this new finding the other way? Despite this abundance of potentially habitable planets, we are yet to be visited by one of our alien neighbours. Does this suggest that there is indeed something unique about the conditions on Earth beyond the composition of our planet and its proximity to the Sun? Even if life did emerge on one of our galactic neighbours, is it likely to have evolved into intelligent organisms?

We want to know your thoughts on this issue, via this week’s Physics World Facebook poll.

Carl Sagan’s Cosmos

Comet Clocked in at Top Angular Velocity Since Discovery

This shows comet C/2009 P1 (Garradd) passing quite close to the star 2 Draconis, located to the left of the comet. This time lapse was shot between 23:32 and 01:13 UTC on March 16-17th, 2009. It slows down shortly after passing the star.