脈動星可能驗證重力波的存在 -- C. Moskowitz - 時事論壇

		時事論壇
		市長：胡卜凱　副市長：
		加入本城市｜推薦本城市｜加入我的最愛｜訂閱最新文章

udn／城市／政治社會／政治時事／【時事論壇】城市／討論區／

你還沒有登入喔( 馬上登入/ 加入會員)

本城市首頁

討論區

精華區

投票區

影像館

推薦連結

公告區

訪客簿

市政中心 (0)


討論區／知識和議題	字體：小中大

看回應文章

脈動星可能驗證重力波的存在 -- C. Moskowitz
瀏覽887｜回應1｜推薦0


	胡卜凱等級：8 留言｜加入好友

Strange Spinning Stars Could Help Prove Einstein Prediction

Clara Moskowitz, Staff Writer, SPACE.com

WASHINGTON -- A newly discovered trove of strange spinning stars in our galaxy could help find evidence for Einstein's prediction of gravitational waves.

The peculiar stars are very dense, strongly magnetic stars called millisecond pulsars, which rotate hundreds of times per second -- faster than a kitchen blender. Seventeen of these objects were recently identified with help from NASA's Fermi space telescope, which scans the skies in high-energy gamma-ray light.

The findings were presented Tuesday at the 215th meeting of the American Astronomical Society in Washington, D.C.

Pulsars are created when massive stars die and collapse in supernova explosions into compact objects made only of neutrons. When roughly the sun's mass is packed into a tiny space about the size of a city, the conserved angular momentum causes the resulting neutron star to spin very rapidly, and to emit a ray of light that sweeps around like a lighthouse beam.

If the pulsar is aligned with Earth, the light beam will cross our planet once every rotation, creating a pulse of light visible at a regular interval of a few milliseconds or seconds, depending on the pulsar's mass. In fact, pulsars are nature's most precise clocks.

Scientists hope that by monitoring the pulse rate of a large network of pulsars over an extended time, they can create a kind of galactic GPS to find evidence for long-sought gravitational waves.

Gravitational waves are theorized fluctuations in the curvature of space-time predicted by Einstein's theory of general relativity. These waves should propagate through space, transporting energy known as gravitational radiation. And gravitational waves could show up as a kind of correlated wiggle in a network of pulsar clocks.

"The Global Positioning System uses time-delay measurements among satellite clocks to determine where you are on Earth," said researcher Scott Ransom of the National Radio Astronomy Observatory in Charlottesville, Va. "Similarly, by monitoring timing changes in a constellation of suitable millisecond pulsars spread all over the sky, we may be able to detect the cumulative background of passing gravitational waves," added Ransom.

The detection of the new objects could greatly aid the search, since millisecond pulsars are relatively difficult to detect -- only about 60 total had been found in the Milky Way before now. Because pulsars shine brightly in gamma-ray light, among other wavelengths, Fermi was able to map a bevy of possible pulsar sources that astronomers then verified with other telescopes.

"Fermi points us to specific targets," said Paul Ray of the Naval Research Laboratory in Washington, D.C. "It's like having a treasure map."

http://news.yahoo.com/s/space/20100105/sc_space/strangespinningstarscouldhelpproveeinsteinprediction;_ylt=Aiw_Kxc6UFxDOg1zUqzmTaMbr7sF

本文於修改第 1 次

引用網址：https://city.udn.com/forum/trackback.jsp?no=2976&aid=3789404

　回應文章

解開地球能存活之謎 -- A. Thompson
	推薦0


	胡卜凱等級：8 留言｜加入好友

How Earth Survived Its Birth

Andrea Thompson, SPACE.com Senior Writer, SPACE.com

WASHINGTON — Just how Earth survived the process of its birth without suffering an early demise by falling into the sun has been something of a mystery to astronomers, but a new model has figured out what protected our planet when it was still a vulnerable, baby world.

In short, temperature differences in the space around the sun, 4.6 billion years ago, caused Earth to migrate outward as much as gravity was trying to pull it inward, and so the fledgling world found equilibrium in what we now know to be a very habitable orbit.

Planets like the Earth are thought to form from condensing clouds of gas and dust surrounding stars. The material in these disks gradually clumps together, eventually forming planetesimals – the asteroid-sized building blocks that eventually collide to form full-fledged planets.

As the planets are forming, they are also thought to migrate within the surrounding dust disk. The classic picture of this planet migration suggests that planets like (and including) the Earth should have plummeted into the sun while they were still planetesimals.

"Well, this contradicts basic observational evidence, like We. Are. Here," said astronomer Moredecai-Mark Mac Low of the American Museum of Natural History in New York.

Mac Low and his colleagues investigated this apparent paradox and came up with a new model that explains how planets can migrate as they're forming and still avoid a fiery premature death. He presented these findings here today at the 215th meeting of the American Astronomical Society.

One problem with the classic view of planet formation and migration is that it assumed that the temperature of the protoplanetary disk around a star is constant in temperature across its whole span, Mac Low explained.

It turns out that portions of the disk are actually opaque and so cannot cool quickly by radiating heat out to space. This creates temperature differences across the disk, and these differences have not been accounted for before in models. So Mac Low and his colleagues created new model simulations of planet migration that include a disk with variations in temperature.

What happens when you change the temperatures in the disk is this: The temperature changes can completely alter the nature of the planet migrations, causing planets to migrate outward instead of inward.

"Well, that is a major development," Mac Low said, because you can put it in the model and see if outward migration cancels inward migration "and allows us to survive, or at least our progenitors."

Sure enough, that seems to be the case. Within the disk, zones of inward and outward migration develop that meet at equilibrium zones; once planets reach these, "they more or less sit there," Mac Low said.

And eventually the disk dissipates to a point where its gravity can no longer influence the planets to pull or push them into new orbits.

So the model suggests that outward migration "allows planetoids to survive," which explain how planets in our solar system and others that we see in galaxy survive, Mac Low said.

http://news.yahoo.com/s/space/20100107/sc_space/howearthsurviveditsbirth;_ylt=Ahkx.mEuxYYPYJmPHRWoW2Ubr7sF

本文於修改第 1 次

引用網址：https://city.udn.com/forum/trackback.jsp?no=2976&aid=3789432

粉絲團