David Letterman made famous his “Top Ten” List. Richard Talcott, a senior editor of Astronomy Magazine created a Top Ten List that Letterman would probably never put on his show. To highlight the 35th anniversary of the magazine, he came up with the “Top Ten Discoveries of the Last 35 Years,” published in Astronomy Magazine, Aug, 2008.

If you ask 10 astronomers for their list, you might get 11 different lists. If you look back over the last 35 years, what would you put on your list as the top discoveries? Before you read on, jot down your list.

Here’re the top ten entries of Talcott’s list:

At #10 is the bar at the center of the Milky Way. Rather than being a simple spiral galaxy, the Milky Way seems to be a barred spiral. This was finally confirmed by observations from Spitzer Space Telescope. The bar extends about 27,000 light years and tilts at an angle of 45 degrees to the line joining the Sun and the Galaxy’s core.

At #9 is the Great Attractor, whose center coincides with the Norma galaxy cluster (Abell 3627). This marks the site of a massive super cluster that may contain as many as 100,000 galaxies and lies 250 million light years from Earth. Our local group of galaxies are moving toward the Virgo cluster, and we and the Virgo cluster are being drawn to the Great Attractor.

At #8 is supernova 1987A. First seen on Feb 24, 1987, this supernova blew up about 160,000 years ago in the Large Magellanic Cloud. It is the closest supernova since the invention of the telescope. The day before the visible explosion, about 10 to the 27 neutrinos tore through the earth, of which detectors saw about 24.

At #7 is the realization that our galaxy and other large galaxies continually gobble up smaller galaxies. Some of the globular clusters in our galaxy may be the remnants of past meals. The Sloan Digital Sky Survey turned up several streams of stars tied to disrupted dwarf galaxies.

At #6 is the family of new objects that create gamma ray bursts. Though first seen by the Vela satellites on July 2, 1967, it wasn’t until Feb 28, 1997 when the BeppoSAX satellite saw the x-ray glow from GRB 970228 and was able to pin point its location in a galaxy that its extra-galactic origin was confirmed. They are the brightest objects in the universe, radiating more energy in a few seconds than the Sun will radiate in its 10-billion-year lifetime. What are they? The consensus is massive supernova collapses, or the conversion of a neutron star into a black hole by continual accretion, or colliding neutron stars.

At #5: Black Holes really exist. This is based on observations from Hubble Space Telescope of the motion of stars and gas clouds at the core of nearby galaxies. In nearly every case, the speeds were too rapid unless there was a highly compressed mass of several millions to billions of solar masses.

At #4: Confirmation of the hyper-expansion period of inflation that occurred “a tiny fraction of a second after the Big Bang” to account for the uniformity of present universe and its flatness. The confirmation was in the form of the micro fluctuations in the cosmic microwave background temperature, measured by the Wilkinson Microwave Anisotropy Probe.

At #3: The incredible voyage of the Voyager spacecraft. These two ships brought back details of not only the outer planets, Jupiter, Saturn, Uranus and Neptune, but more importantly, many of their moons. They revealed Io, as volcanically active and Callisto, the solar system’s most cratered body. Titan’s atmosphere is nitrogen rich with a pressure 50% greater than ours. Voyager 2 found Uranus and Neptune to have magnetic fields and rings.

At #2: Planets by the hundreds. Starting in 1995 with the discovery of a planet around the Sun-like star 51 Pegasi, there are now more than 300 known exoplanets, Though most of these are limited to being “hot Jupiters” because of the sensitivity range of the current detection methods, some have been found to be smaller than Neptune.

And at #1 is: Dark Energy, the force that may determine the entire universe’s fate. In 1998, two groups reported on the Hubble observations of Type Ia supernova, white dwarfs that are part of a binary system that went supernova after inhaling enough of their companion to tip their mass above 1.4 solar masses. This precision candle allows precision distance determination from the measured luminosity. The result: the fainter supernova were farther than their red shift distances implied. One explanation: a new force is accelerating the universe’s expansion- dark energy.

So what’s on your list?

Published in Nov 2008 Cosmic Messenger