Summary of Scientific Results - 2007
Subaru’s journey of exploration utilizes the inherit quest for knowledge as thedriving principle behind its mission to explore the Universe more deeply andcomprehend nature more fully. As the universe continues to change and ourunderstanding evolves accordingly, wondrous opportunities for discovery present
themselves. Employing the latest technologies, we extended our gaze furtherand deeper into the sky towards the beginning of time, achieving results thatwere once considered science fiction.
During 2007, there were many astounding moments of discovery at the Subaru
Telescope ranging from the smallest of micro-meteoroids flashing through ournight sky to binary stars in nearby galaxies to the first mapping of dark matter.
Let us briefly examine what some of those magical discoveries entailed.
Researchers evaluated the diameters of the heated tunnels left behind as
meteors passed through the upper atmosphere. They estimated the meteors tobe less than a millimeter in size and the typical column width of a meteor track as
narrow as a few millimeters. This study was a bi-product of wide-field imagingobservations and was the first time a meteor track column has been precisely
measured using a physical analysis of the light emitted during the event. For thefuture, by focusing the Subaru Telescope to the altitude of the upper atmosphere
where meteors disintegrate, highly detailed images of faint meteors can becollected to further the study of micro-meteoroids.
Outside the earth’s atmosphere, Subaru monitored the demise of a comet as it
broke into smaller and smaller pieces. Comet 73P/Schwassman-Wachmann 3(SW3) was first discovered in 1930. In 1995, SW3 became exciting when thecomet began breaking apart. When SW3 was observed again in 2000 it had
further fragmented, and by the time the comet came around again in 2006, there
were dozens of pieces. If the current collection of comet fragments remains
stable, the team will continue to track them to understand the evolution of cometfragments and the gases and ices they contain. If the comet continues
disintegrating some of those pieces may eventually become meteors.
While we’re discussing comets, analysis of Subaru’s observations of NASA’s
Deep Impact event (July 2005) showed that comet 9P/Tempel 1 consists of corematerial that has not metamorphosed since this comet left the Kuiper belt region
beyond Neptune. This finding means that comets may maintain their central
integrity even after numerous perihelion passages around the sun, which isimportant because cometary nuclei contain primordial dust and ice that existed
when the solar system was first forming.
Subaru has a powerful wide-field camera mounted in the prime focus position
called Suprime-Cam, and images of familiar objects provide discovery andinsight into previously unseen phenomenon. A new image of the Crab Nebula(M1) supernova remnant was taken in March 2007, highlighting the beauty ofstellar debris expanding away from the site of this ancient blast (first observed in1054). The clarity and resolution of this image gives astronomers opportunities tostudy the mechanics of the expanding gas in the nebula in detail much greaterthan before.
Over the past several years, more and more planets have been discoveredaround nearby stars. Several months ago, a Japanese/US collaboration
observed planetary system TrES-1, and measured the angle between the stellar
spin axis and the planetary orbital axis to diagnose and discern the planet
formation mechanisms. It was the third case for which the spin-orbit alignmenthas been measured, and importantly it is the faintest target (magnitude 12) todate. The team demonstrated for the first time that such measurements arepossible for such a faint object, which is significant because most of the newly
discovered transiting planets have relatively faint host stars. What is interesting
about this system is that you have a Jupiter-sized planet that orbits very close to
its star, much closer and faster than the planet Mercury in our solar system.
As planets are being discovered around nearby stars, stars are also being foundaround neighboring stars. In February 2007, an international research teamobtained the first images of the second "sun" around the star gamma Cephei.
This direct detection significantly improves our knowledge of the gamma Cephei
system, such as the masses of the two stars and the minimum mass of theircompanion planet. Another research event later in the year collected an imageof a young binary star system called XZ Tauri that revealed for the first time a jetof material streaming away from the pair's primary star. A previous observation
showed a jet streaming from the secondary star; however, this new jet is offset
by about 30 degrees from the secondary one. The discoveries suggest that eachstar could have a circumstellar disk with sites of planetary formation hidden
inside. What is significant about binary star research is that binaries provide thebest method for astronomers to determine the mass of distant stars. Additionally,
because a large proportion of stars exist in binary systems, these stars help usunderstand the processes by which all stars form. The difficulty with studying
these systems is that frequently the primary star occults the secondary one due
to its brightness and/or the binary system located too far away to resolve clearly.
As the Subaru Telescope peered further a field, astronomers detected the heavy
element thorium in a red giant star (COS82) within the Ursa Minor dwarf galaxy,a satellite of the Milky Way. Their discovery marks the first detection of thorium(232Th) in a star beyond the Milky Way, and follows the identification of thoriumin more than ten stars within the Milky Way. What makes thorium important isthat it is radioactive like uranium, and astronomers and can use these heavy
elements to deduce the stars’ ages, which may be millions or billions of years;
this approach is called radioactive cosmochronometry. Other firsts included thediscovery of an unusual streak of ionized hydrogen gas associated with Galaxy
D100 located approximately 300 million light-years from Earth. The filament ofgas is only 6 thousand light-years wide, yet extends 200,000 light-years, about
the distance between the Milky Way Galaxy and its companion, the Large
Magellanic Cloud. Finding such an extremely narrow and long ionized gas cloudis a first in astronomy. Other galactic research included a thorough inspection ofa galaxy building block. Astronomers found that a small spheroidal dwarf galaxy
named Leo II largely consists of older stars, a sign of survival through galactic
cannibalism under which massive galaxies (i.e. Milky Way) consume smaller
galaxies to attain their extensive size.
To close out the year, astronomers from Japan obtained deep field and highresolution images of galaxies from 11 billion years ago. Their initial findings
showed that concentrated elliptical galaxies formed from the collision andmerging of extended disk galaxies between 11 and 8 billion years ago and thatthe evolution of the galaxies is much milder between the present and 8 billion
years ago than between 11 and 8 billion years ago.
As our vision outward reached further back in time, an international team ofastronomers created a three-dimensional map of the universe that provides thefirst direct look at the large-scale distribution of matter. This is the best evidence
yet that “normal” matter, like stars and galaxies, accumulate along the densest
concentrations of invisible dark matter. The map extends to a time when theuniverse was only half its current size and shows that dark matter has grownincreasingly clumpy, forming long thread-like structures, the further away fromthe Big Bang.