Jul 10, 2010

Star in birth reportedly witnessed

As­tro­no­mers are re­port­ing that they have glimpsed what could be the youngest known star at the mo­ment of its birth.

Not yet de­vel­oped in­to a true star, the ob­ject has just be­gun pulling in mat­ter from a sur­round­ing en­ve­lope of gas and dust, ac­cord­ing to a new study that ap­pears in the cur­rent is­sue of The As­t­ro­phys­i­cal Jour­nal.

A star-forming re­gion si­mi­lar to the one where astro­nomers say they have found a star in its ear­li­est stages of for­ma­tion. The re­gion pic­tured above is known as the Orion-KL re­gion. (Pho­to: NA­SA, ESA)

The au­thors found the ob­ject us­ing the Spitzer Space Tel­e­scope and the Sub­mil­lime­ter Ar­ray tel­e­scope in Ha­waii. It lies in the Per­seus star-form­ing re­gion, about 800 light years away with­in our Milky Way gal­axy. (A light-year is the dis­tance light tra­vels in a year).

Stars form out of large, cold, dense re­gions of gas and dust called mo­lec­u­lar clouds, which pep­per the gal­axy.

As­tro­no­mers think the new­found ob­ject is in be­tween its pre­stel­lar phase, when a par­tic­u­larly dense re­gion of a mo­lec­u­lar cloud first be­gins to clump to­geth­er, and the pro­to­star phase, when gra­vity has pulled enough ma­te­ri­al to­geth­er to form a dense, hot co­re out of the sur­round­ing en­ve­lope.

“It’s very dif­fi­cult to de­tect ob­jects in this phase of star forma­t­ion, be­cause they are very short-lived and they emit very lit­tle light,” said Xue­peng Chen, a post­doc­tor­al as­so­ci­ate at Yale Uni­vers­ity and lead au­thor of the pa­per. The team de­tected the faint light emitted by the dust sur­round­ing the ob­ject.

Most pro­to­stars are be­tween one to 10 times as lu­mi­nous as the Sun, with large dust en­ve­lopes that glow in in­fra­red light, a low-energy form of light not vis­i­ble to the un­aided eye.

Be­cause the new ob­ject, dubbed L1448-IRS2E, is less than one tenth as lu­mi­nous as the Sun, the as­tro­no­mers be­lieve it’s too dim to be a true pro­to­star. Yet they al­so found it’s eject­ing streams of high-speed gas from its cen­ter, con­firm­ing, they said, that some sort of pre­lim­i­nar­y mass has formed and the ob­ject is be­yond its pre­stel­lar phase. This kind of out­flow is seen in pro­to­stars as a re­sult of the mag­net­ic field sur­round­ing the form­ing star, but has not been seen at such an early stage un­til now.

The team hopes to use the new Hers­chel space tel­e­scope, launched last May, to look for more of these ob­jects caught be­tween the ear­li­est stages of star forma­t­ion so they can bet­ter un­der­stand how stars grow and evolve. “Stars are de­fined by their mass, but we still don’t know at what stage of the forma­t­ion pro­cess a star ac­quires most of its mass,” said Yale’s Héc­tor Ar­ce, an­oth­er au­thor of the pa­per. “This is one of the big ques­tions driv­ing our work.”

The re­search group al­so in­cludes as­tro­no­mers from the Har­vard-Smith­son­ian Cen­ter for As­t­ro­phys­ics in Cam­bridge, Mass. and the Max Planck In­sti­tute for As­tronomy in Hei­del­berg, Ger­ma­ny.



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