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Star with vast tail astonishes scientists

Aug. 15, 2007
Courtesy NASA
and World Science staff

A NASA craft has spot­ted a sur­pris­ingly long com­et-like tail be­hind a star streak­ing through space at su­pe­r­son­ic speeds. 

“This is an ut­terly new phe­nom­e­non to us, and we are still in the pro­cess of un­der­stand­ing the phys­ics in­volved,” said Mark Seib­ert of the Ob­ser­va­to­ry of the Car­ne­gie In­sti­tu­tion of Wash­ing­ton in Pas­a­de­na, Ca­lif.. 

This im­age is a mo­sa­ic made up of in­di­vid­u­al im­ages tak­en by the far-ul­t­ra­vio­let light de­tec­tor on NA­SA's Gal­axy Ev­o­lu­tion Ex­plor­er in No­vem­ber and De­cem­ber, 2006. (Cred­it: NA­SA/JPL-Cal­tech)
“We hope to be able to read Mi­ra’s tail like a tick­er tape to learn about the star’s life,” added Seib­ert, co-au­thor of a pa­pe­r de­scrib­ing the find­ings. Mi­ra would be in a sense the first real “shoot­ing star” known—since the streaks of light tra­di­tion­ally called shoot­ing stars are really me­te­ors, or rocks fall­ing through the at­mos­phere.

The star, named Mi­ra af­ter the Lat­in word for “won­der­ful,” has been a fa­vor­ite of as­tro­no­mers for ap­prox­i­mately 400 years. It is a fast-mov­ing, old­er red gi­ant that is shed­ding mas­sive amounts of sur­face ma­te­ri­al.

It’s “a­maz­ing to dis­cov­er such a startlingly large and im­por­tant fea­ture of an ob­ject that has been known and stud­ied for more than 400 years,” said James D. Neill of the Cal­i­for­nia In­sti­tute of Tech­nol­o­gy In Pas­a­de­na, Ca­lif. The in­sti­tute leads the mis­sion for NA­SA’s Gal­axy Ev­o­lu­tion Ex­plor­er space­craft.f

The craft scanned the pop­u­lar star dur­ing an on­go­ing sky sur­vey. As­tro­no­mers then no­ticed what looked like a com­et with a gi­ant tail. Ma­te­ri­al blow­ing off Mi­ra is form­ing a wake 13 light-years long, or about 20,000 times the av­er­age dis­tance of Plu­to from the sun. Noth­ing like this has been seen be­fore around a star.

“I was shocked when I first saw this com­pletely un­ex­pected, hu­mon­gous tail trail­ing be­hind a well-known star,” said Cal­tech’s Chris­to­pher Mar­tin. “It was amaz­ing how Mi­ra’s tail ech­oed on vast, in­ter­stel­lar scales the fa­mil­iar phe­nom­e­na” such as the stream of gas be­hind a je­t or a speed­boat’s tur­bu­lent wake. 

Mar­tin is prin­ci­pal in­ves­ti­ga­tor for the space­craft and lead au­thor of the pa­pe­r, in the Aug. 15 edi­tion of the re­search jour­nal Na­ture. 

As­tro­no­mers say Mi­ra’s tail of­fers a un­ique op­por­tun­ity to study how stars like our sun die and ul­ti­mately seed new so­lar sys­tems. As Mi­ra hur­tles along, its tail sheds car­bon, ox­y­gen and oth­er im­por­tant el­e­ments needed to form new stars, plan­ets and pos­sibly even life. This tail ma­te­ri­al, vis­i­ble for the first time, has been re­leased dur­ing the past 30,000 years.

Bil­lions of years ago, Mi­ra was si­m­i­lar to our sun. Over time, it be­gan to swell in­to what is called a varia­ble red gi­ant—a pul­sat­ing, puffed-up star that pe­r­i­od­ic­ally grows bright enough to see with the na­ked eye. Mi­ra eventually will eject all its re­main­ing gas in­to space, form­ing a col­or­ful shell called a plan­e­tary neb­u­la, as­tro­no­mers say. The neb­u­la will fade with time, leav­ing only the burnt-out co­re of the orig­i­nal star, which will then be called a white dwarf.

Com­pared to oth­er red gi­ants, Mi­ra is trav­el­ing un­usu­ally fast, pos­sibly due to boosts from the gra­vity of pass­ing stars, in­ves­ti­ga­tors said. It plows along at an es­ti­mat­ed 291,000 miles per hour. Rac­ing along with it is a small, dis­tant com­pan­ion thought to be a white dwarf. The pair, al­so known as Mi­ra A (the red gi­ant) and Mi­ra B, or­bit slowly around each oth­er as they trav­el to­geth­er in the con­stella­t­ion Ce­tus, 350 light-years from Earth.

In ad­di­tion to Mi­ra’s tail, the space­craft al­so found a bow shock, a type of build­up of hot gas, in front of the star, and two sin­u­ous streams of ma­te­ri­al em­a­nat­ing from the star’s front and back. As­tro­no­mers think hot gas in the bow shock is heat­ing the gas blow­ing off the star, caus­ing it to flu­o­resce with ul­tra­vi­o­let light. This glow­ing ma­te­ri­al then swirls around be­hind the star, cre­at­ing a tur­bu­lent, tail-like wake. The pro­cess is si­m­i­lar to a speed­ing boat leav­ing a chop­py wake or a steam train pro­duc­ing a trail of smoke.

Mi­ra’s tail only glows with ul­tra­vi­o­let light, a type of light more en­er­get­ic than that vis­i­ble to the eye, which might ex­plain why oth­er tele­scopes have missed it, re­search­ers said. The Gal­axy Ev­o­lu­tion Ex­plor­er is very sen­si­tive to such light and al­so has an ex­tremely wide field of view, so it can scan the sky for un­usu­al ul­tra­vi­o­let ac­ti­vity.

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A NASA craft has spotted a surprisingly long comet-like tail behind a star streaking through space at supersonic speeds. “This is an utterly new phenomenon to us, and we are still in the process of understanding the physics involved,” said Mark Seibert of the Observatories of the Carnegie Institution of Washington in Pasadena, Calif.. “We hope to be able to read Mira’s tail like a ticker tape to learn about the star’s life,” added Seibert, co-author of a paper describing the findings. Mira would be in a sense the first real “shooting star”—since normally seen “shooting stars” are really meteors, or rocks falling through the atmosphere. The star, named Mira after the Latin word for “wonderful,” has been a favorite of astronomers for approximately 400 years. It is a fast-moving, older red giant that is shedding massive amounts of surface material. It’s “amazing to discover such a startlingly large and important feature of an object that has been known and studied for more than 400 years,” said James D. Neill of the California Institute of Technology In Pasadena, Calif. The institute leads the misson for NASA’s Galaxy Evolution Explorer spacecraft. The craft scanned the popular star during an ongoing sky survey. Astronomers then noticed what looked like a comet with a giant tail. Material blowing off Mira is forming a wake 13 light-years long, or about 20,000 times the average distance of Pluto from the sun. Nothing like this has been seen before around a star. “I was shocked when I first saw this completely unexpected, humongous tail trailing behind a well-known star,” said Caltech’s Christopher Martin. “It was amazing how Mira’s tail echoed on vast, interstellar scales the familiar phenomena” such as the stream of gas behind a jet or a speedboat’s turbulent wake. Martin is principal investigator for the spacecraft and lead author of the paper, in the Aug. 15 edition of the research Nature. Astronomers say Mira’s tail offers a unique opportunity to study how stars like our sun die and ultimately seed new solar systems. As Mira hurtles along, its tail sheds carbon, oxygen and other important elements needed to form new stars, planets and possibly even life. This tail material, visible for the first time, has been released during the past 30,000 years. Billions of years ago, Mira was similar to our sun. Over time, it began to swell into what is called a variable red giant—a pulsating, puffed-up star that periodically grows bright enough to see with the naked eye. Mira eventually will eject all its remaining gas into space, forming a colorful shell called a planetary nebula, astronomers say. The nebula will fade with time, leaving only the burnt-out core of the original star, which will then be called a white dwarf. Compared to other red giants, Mira is traveling unusually fast, possibly due to boosts from the gravity of passing stars, investigators said. It plows along at an estimated 291,000 miles per hour. Racing along with it is a small, distant companion thought to be a white dwarf. The pair, also known as Mira A (the red giant) and Mira B, orbit slowly around each other as they travel together in the constellation Cetus, 350 light-years from Earth. In addition to Mira’s tail, the spacecraft also found a bow shock, a type of buildup of hot gas, in front of the star, and two sinuous streams of material emanating from the star’s front and back. Astronomers think hot gas in the bow shock is heating the gas blowing off the star, causing it to fluoresce with ultraviolet light. This glowing material then swirls around behind the star, creating a turbulent, tail-like wake. The process is similar to a speeding boat leaving a choppy wake or a steam train producing a trail of smoke. Mira’s tail only glows with ultraviolet light, a type of light more energetic than that visible to the eye, which might explain why other telescopes have missed it, researchers said. The Galaxy Evolution Explorer is very sensitive to such light and also has an extremely wide field of view, so it can scan the sky for unusual ultraviolet activity.