Star with vast tail astonishes scientists

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..

“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.

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)


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.

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.