Yale Bulletin and Calendar

October 24, 2003|Volume 32, Number 8















Graduate School Dean Peter Salovey (left) hosted the lecture by astronomer Charles Bailyn as part of the Graduate School's "In the Company of Scholars" series.

Astronomer's talk brings mysterious
cosmos to an earthly level

Unlike most scientists, astronomers can't conduct their experiments in the lab or get close to what they study in the field -- they "are obliged to sit back and watch from a distance," said Charles Bailyn, chair of the astronomy department, when he spoke about the paradox of "Observing the Invisible Cosmos" on Oct. 16 at the Graduate School.

His talk, the first lecture in this year's "In the Company of Scholars" series, included colorful photos of stars, galaxies and even presumed "empty spots" in the sky that turned out to be star-studded when observed with the right equipment over enough time.

"Everywhere you look in the sky, it's covered with galaxies," Bailyn said.

Because the talk was directed at non-astronomers, Bailyn began with the basics. "Everything we know about our universe, we know from observing photons," he said, explaining that photons are light waves that, under some circumstances, behave like particles. Stars emit photons, which travel across millions of miles of space towards Earth, where they may be seen through telescopes like the one Yale shares with two other universities at Cerro Tololo in the Chilean Andes, he noted.

Ground-based telescopes like the one in Chile have optics that allow astronomers to view large areas of sky and photograph vast objects like the Andromeda Galaxy -- our nearest galactic neighbor, he said. Space-based telescopes like the Hubbell are best used for precision observations of small areas deep in space, Bailyn explained.

But some celestial phenomena -- extra-solar planets, black holes and dark matter, in particular -- can't be observed through telescopes at all, and yet astronomers are certain of their existence, he noted. "What right do I have, as an observational scientist, to say I know about these things, when I can't see them?" he asked.

The answer, he said, involves classical physics. Using long-established principles like the Doppler shift and orbital dynamics as explained by Johannes Keppler (1571-1630) and Isaac Newton (1643-1727), astronomers are able to take some measurements from observation and use them in equations to calculate non-observable data, he explained. Velocity, distance from Earth, orbital period and mass are interconnected in well-established ways, Bailyn noted, and if scientists have enough data to plug into the equations, they can deduce the missing information. "We can figure out the mass of a hidden object, for example," he said.

Planets that revolve around other suns can't be seen, because they are too faint and have orbits so close to their stars that they don't show up in telescopes, he said. Nonetheless, the Yale scientist noted, by measuring the Doppler shift of a star relative to its invisible planet, astronomers have been able to identify over 100 planets beyond our solar system -- all of them at least as big as Jupiter.

The presence of black holes and dark matter ("something so weird we don't know what to call it," Bailyn quipped) can also be established by plugging data from observable phenomena into the formulas of classical physics, according to the astromer. Scientists have determined in this way that all galaxies have black holes in their middle and a halo of dark matter surrounding them, he said.

Astronomers, contended Bailyn, are good at discovering what can't be seen, and they are clever when they get around to naming it. Some maintain that dark matter is actually Weakly Interacting Massive Particles (WIMPs), he noted, while others hold that dark matter is made up of Massive Astrophysical Compact Halo Objects (MACHOs). Either way, 25% of the universe is composed of this still-unknown dark matter, he added.

And that's not the biggest mystery, said Bailyn, noting that about 70% of the universe is composed of "dark energy." Dark matter has mass, and "pulls stuff together," he explained, while dark energy is a force that pushes things apart. Even less is known about dark energy than about dark matter or black holes, the Yale scientist told the audience, adding that, in fact, astronomers have a lot of universe to explore in the years ahead.

According to Bailyn, although tens of millions of stars are currently being studied, "We don't know what 90% of matter in the galaxy is. We know it's there, but we don't know what it is."

Bailyn, who joined the Yale faculty in 1990, is a Yale alumnus, having earned his B.S. in astronomy and physics from Yale College in 1981. His talk was hosted by Peter Salovey, dean of the Graduate School, and sponsored by the Kenneth Gerber Memorial Fund. Each of the lectures in the "In the Company of Scholars" series presents current research to a broad, inter-disciplinary audience. The next speaker will be Christopher Wood, professor of the history of art, who will present "The Fabrication of Facts, circa 1520" on Tuesday, Nov. 4, at 4 p.m. in the McDougal Center, Rm. 119 of the Hall of Graduate Studies, 320 York St.

-- By Gila Reinstein


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Campus Notes

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