The Impact of 2MASS

2MASS scientists have discovered the existence of very cool dwarf stars and star-like objects, cooler than what was previously known. They have dubbed these objects "L-type dwarfs". Recently, they have also confirmed the existence of brown dwarfs, rich in atmospheric methane. These "T-type dwarfs", as they have been called, barely contain more mass than Jupiter. A nearby example is a companion, indicated at left by the arrow, to the star Gleise 570. The faint T dwarf appears very blue in the near-infrared, much like the planets Uranus and Neptune do. An artist's rendition of the Gleise 570 system is at right. Both L dwarfs and T dwarfs are so low in mass that they cannot produce internal energy as our Sun does, by thermonuclear fusion. Instead, they shine, mostly in the infrared, by slowly collapsing under their own weight. Together, L dwarfs and T dwarfs are twice as numerous in the Milky Way Galaxy as full-fledged stars, like our Sun.

2MASS scientists have also discovered new galaxies in the plane of our Milky Way Galaxy. Away from the plane of our Galaxy, other galaxies are seen pretty much uniformly distributed across the sky (although, astronomers know that galaxies clump together in loose groupings and clusters throughout the Universe). In the so-called "Zone of Avoidance", astronomers optically see very few galaxies, since the obscuring dust in the plane of our Milky Way hides galaxies from view. But, in the near-infrared, many more galaxies are detected in the plane. At left is a recent discovery of a spiral galaxy, probably much like our own Milky Way, seen off in the distance, but through the murky dust. The ability for 2MASS to penetrate through our Galaxy's dust means astronomers can now more accurately count the number of galaxies in our local Universe.

In addition, for galaxies away from the Galactic plane that astronomers already knew about, distances to a large number of these galaxies can now be estimated, combining their 2MASS near-infrared brightnesses with radio telescope observations of the way these galaxies rotate. From these distances, out to about 3 billion light years, astronomers can better understand the actual distribution of galaxies in the local Universe, which tells us a lot of how galaxies formed and evolved since the Big Bang.

2MASS also offers an unprecedented view of the Milky Way, nearly free of the obscuring effects of dust, revealing the true distribution of the luminous mass in our Galaxy, and thus, the largest structures, over the entire extent of the Galaxy. In other words, 2MASS will produce a map of our home Galaxy at high resolution, never before accomplished at optical wavelengths. Many more fascinating discoveries and insights await to be made by astronomers all over the world, using the 2MASS catalogs and images, as the first large offering of 2MASS data has hit the Internet. We anticipate that 2MASS will have lasting and continuing value to astronomers, much as the Palomar optical all-sky survey has, long after the survey is complete.

Finally, 2MASS lays the groundwork for future infrared NASA missions that will peer into the sky at mid-infrared and far-infrared wavelengths. To demonstrate this, let's take a closer look at the center of our Galaxy. Below are three panels, showing, at approximately the same scale and location, the view of the center at optical wavelengths (left), the near-infrared 2MASS view (middle), and the view by the IRAS satellite, the old prototype for the future mid- and far-infrared missions (right).

POSS	2MASS	IRAS
Optical	Near-Infrared	Far-Infrared

As you can see, the Galaxy's center is completely invisible at optical wavelengths. But, 2MASS is revealing for the first time extraordinary details about the center and its larger-scale environment. IRAS saw even more structure, in the form of cool stars, nebulae, and dust, warmed by starlight, albeit at pretty low resolution (see how fuzzy and blobby the structures appear). Future airborne and space-based infrared missions, such as SOFIA, SIRTF, and NGST will build upon what was learned almost twenty years ago by IRAS, and use the unprecendented detail of the 2MASS near-infrared digital image atlas to plan for and understand what these missions observe. Altogether, the infrared astronomy of today, through 2MASS, and tomorrow, will give us a much richer and complete understanding of our Universe.

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