“I Am Oz, The Great and Powerful…”
May 12, 2011
When the Wizard of Oz roared that line, he was hidden behind a curtain. He knew all too well that he was not particularly great nor very powerful, and wanted no one to find out (a scheme foiled by that heroic terrier Toto). The opposite problem exists at the W. M. Keck Observatory. There is genuinely great cosmic stuff being discovered with the world’s largest, optical and infrared telescopes – so ‘great’ and ‘powerful’ apply – but to many folks it all seems hidden behind a curtain.
There is no curtain, of course, as anyone knows if they have poked around the Keck Observatory Visitor Center in Waimea. But to banish even the shadow of any Oz-like shenanigans, here is a quick, easy-to-digest, summary of a few recent bona fide feats of Keck wizardry, including the discovery of the coldest star, the brightest star and a glimpse into the uncharted depths of Jupiter.
Some have called it the hot chocolate star. Others prefer coffee or tea. Whatever your taste, the dim brown dwarf star discovered in March with the surface temperature of a hot beverage is the latest candidate for the dubious title of ‘coldest star known.’
Why dubious? Because this brown dwarf is so cool, it begins to cross the blurry line between small cold stars and big, hot, super-Jupiter-like planets. Brown dwarfs are essentially failed stars: they lack the mass and gravity to trigger the nuclear reactions that make stars shine.
The newly discovered brown dwarf identified as CFBDSIR 1458+10B, is the smaller and dimmer member of a double brown dwarf system located just 75 light-years from Earth. The lesser dwarf has a temperature of about 370 K. That translates into about 200 degrees F (100 degrees C), or just below the boiling point of water on Earth’s surface. CFBDSIR 1458+10B was detected using the Laser Guide Star (LGS) Adaptive Optics system on the 10-meter Keck II telescope. Adaptive Optics essentially cancels out much of Earth’s atmospheric interference.
“The binary was resolved with Keck LGS Adaptive Optics imaging, and in fact can only be done with Keck LGS, given the difficulty of the measurement,” said University of Hawaii astronomer Michael Liu, who led the team which made the discovery.
Liu and his colleagues also used special instruments on the Canada-France-Hawaii Telescope to determine the distance to the brown dwarf duo – an essential step for interpreting what they saw with the Keck telescope.
At the extreme opposite end of the stellar spectrum from cold brown dwarfs is a spectacular supernova known as SN2008am. At its peak brightness, three years ago, it was over 100 billion times brighter than the Sun. It emitted enough energy in one second to satisfy the power needs of the United States for one million times longer than the universe has existed.
There is no sense in trying to get your head around such an unimaginably huge amount of power. Suffice it to say that for a little while SN2008am was the most luminous star ever known. Luckily this colossal outburst of energy happened in a galaxy far, far away (3.7 billion light-years). So instead of deep-frying Earth in a searing bath of x-rays and gamma rays, it was only visible with telescopes.
Supernovae (that’s plural for supernova) are generally the brightest stars in the universe – appearing suddenly and briefly as ‘new’stars as they reach peak brightness. Nova means new. Ironically, supernovae are actually large stars in the violent throes of death. In the case of SN2008am, it is an elite member of the supernova class; what’s called a super-luminous supernova.
Immediately after SN2008am was detected by University of Texas astronomers Emmanouil “Manos” Chatzopoulos and J. Craig Wheeler last year, a number of telescopes and instruments, including the Keck I Telescope’s Low Resolution Imaging Spectrometer (LRIS), were quickly slewed into position to gather detailed data.
The new data, reported last month in The Astrophysical Journal, reveal that the extreme brightness of this supernova is probably caused by a double whammy effect. The initial supernova explosion of the dying star sent out a shockwave that slammed into a shell of debris that had been previously burped-up from the nauseous, dying star. That collision lit up too, pushing the supernova to super-luminosity.
THE CASE OF JUPITER’S MISSING BELT
Back home in our comparatively peaceful solar system, Jupiter has also been an object of interest to Keck astronomers. Early last year one of the largest of the belts that wrap around Jupiter from pole to pole went on vacation, took a powder, vamoosed, i.e., disappeared. This year that “South Equatorial Belt” appears to be slowly coming back. The secret to its strange behavior has now been discovered thanks to the Keck II telescope’s Adaptive Optics system and the clever use of Jupiter’s icy moon Europa.
Here’s how it happened: Normally, Keck astronomers use a powerful laser to create an artificial guide star with which they measure the distortions to starlight caused by Earth’s atmosphere. Those distortions are then canceled with Adaptive Optics. But Jupiter is much brighter than the laser guide star. Astronomers needed something comparably bright that was also very close to Jupiter in the sky. On November 30, 2010, Jupiter’s icy moon Europa was positioned just right to serve that purpose.
On that date UC Berkeley astronomer Mike Wong, with the assistance of Keck support astronomer Randy Campbell, captured images of Jupiter in four different bands of infrared light. One of those, the 5-micron thermal infrared band, showed the heat of Jupiter itself shining up through the cloud layers.
“The thermal infrared senses breaks in the cloud cover,” said Wong. When astronomers put all the infrared pictures together and compared them to visible light images, they got a glimpse of a thinning, breaking layer of high, bright, icy clouds that have obscured the brown-red South Equatorial Belt for about a year.
So the missing belt wasn’t really missing at all. It was just lying low; hiding behind a curtain of clouds. Just another curtain that Keck astronomers, true to Toto’s legacy, pulled aside to unmask a secret.