Comet-like Tail Discovered Behind Speeding Star

[Snowden]

Comet-like Tail Discovered Behind Speeding Star
By Ker Than
Staff Writer
posted: 15 August 2007
01:01 pm ET
This story was updated at 1:50 pm EDT.

A dying star hurtling through space has left a comet-like tail that reveals its history stretching back 30,000 years.

"This is an utterly new phenomenon to us, and we are still in the process of understanding the physics involved," said study team member Mark Seibert of the Carnegie Observatories in Pasadena, California. "We hope to be able to read Mira's tail like a ticker tape to learn about the star's life."

The red-giant star, called Mira A, is streaming a comet-like tail behind it that is 13-light-years long-thousands of times the breadth of our solar system. A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion kilometers). The tail is like a glowing bread-crumb trail in the sky showing the star's movements for the past 30 millennia, during which time it has shed large stores of carbon, oxygen and other elements.

"If Neanderthal man had ultraviolet eyes and could look above the atmosphere, he could have seen the beginning of this tail forming," study leader Chris Martin, an astronomer at Caltech, said in a teleconference Wednesday.

The researchers think Mira's tail might have once been much longer. "It may be that the tail slowly fades with time and we just can't see it because it's below our sensitivity level," Martin said."[Or] it may be that the star has moved into a region of the interstellar medium that is denser, and that makes the tail light up more."

Our own sun will one day become a red giant, so the finding, detailed in the Aug. 16 issue of the journal Nature, could provide valuable clues about the fate of our solar system and how stars' cast-off remains become seeds for new stars, planets and possibly even life.

A pulsing star

Located about 350 light-years from Earth, Mira is a so-called variable star that pulsates from dim to bright over a period of about 330 days. At its brightest, Mira A is visible to the naked eye. Traveling alongside Mira A is another star, either a white dwarf or a smaller version of our sun, called Mira B.

The two stars are separated by about 90 astronomical units (AU), with one AU being equal to the distance between the Earth and the sun. A previous study suggested that dust shed by Mira A is accreting into a ring around Mira B and could one day become the raw material for new planets.

The stellar pair is barreling through space at a swift 291,000 mph (468,000 kilometers per hour), possibly speeded along in their journey by occasional gravity boosts from other passing stars.

"Mira is racing through space like a speeding bullet, although it's actually 300 times faster than a bullet goes on earth," Martin said.
Scientists spotted Mira A's tail of streaming gas while using the Galaxy Evolution Explorer, an Earth-orbiting telescope, to survey the sky in ultraviolet light. Nothing of its kind has ever been observed around a star.

Visible only in UV

The streaming tail is only visible in the far ultraviolet, which might explain why it's never been seen before despite the fact that astronomers have known about Mira A for about 400 years. "We never have predicted a turbulent wake behind a star that glows only with ultraviolet light," Seibert said.

Mira A was once a star like our sun. As it aged and lost the hydrogen fuel needed to stoke its internal fires, the star swelled into a pulsating red giant. Eventually, Mira A will eject all of its remaining gas into space, forming a colorful cloud around it called a planetary nebula. This too will fade in time, and Mira A will shrivel into a burnt-out white dwarf.

The Galaxy Evolution Explorer, a project of NASA, also spotted a buildup of hot gas, called a bow shock, in front of the star, as well as two thin filaments of material coming out of the star's front and back.

Astronomers think the hot gas in the bow shock is heating up the gas blowing off the star, creating a trailing tail that glows in the ultraviolet.

Michael Shara, a curator in the Department of Astrophysics at the American Museum of Natural History in New York City, called the new discovery "really remarkable."

"We're seeing ourselves," Shara said. "We are seeing in a sense the process that the sun will go through in a about 4 or 5 billion years when it starts to run out of fuel and its core turns into a red giant and starts to shed material. It's also in a sense looking at where we come from. It's our origins. All the carbon in our muscles and the oxygen that we breathe everytime we take a breath comes from red giant stars."

SPACE.com -- Comet-like Tail Discovered Behind Speeding Star

[Snowden]

Astronomers surprised by star with comet-like tail

Wed Aug 15, 2007 6:12PM EDT

By Will Dunham

WASHINGTON (Reuters) - A large star in its death throes is leaving a huge, turbulent tail of oxygen, carbon and nitrogen in its wake that makes it look like an immense comet hurtling through space, astronomers said on Wednesday.

Nothing like this has ever previously been witnessed in a star, according to scientists who detected it using NASA's Galaxy Evolution Explorer, an orbiting space telescope that observes the cosmos in ultraviolet light.

This tail, spanning a stunning distance of 13 light-years, was detected behind the star Mira, located 350 light-years from Earth in the "whale" constellation Cetus.

"There's a star with a tail in the tail of the whale," said one of the researchers, astronomer Mark Seibert of the Observatories of the Carnegie Institution of Washington in Pasadena, California.

A light year is about 6 trillion miles, the distance light travels in a year.

Rocketing through our Milky Way galaxy at 80 miles per second (130 km per second) -- literally faster than a speeding bullet -- the star is spewing material that scientists believe may be recycled into new stars, planets and maybe even life.

"We believe that the tail is made up of material that is being shed by the star which is heating up and then spiraling back into this turbulent wake," said astronomer Christopher Martin of California Institute of Technology, one of the researchers in the study published in the journal Nature.

Mira is a so-called "red giant" star near the end of its life. Astronomers believe our sun will become a similar red giant in 4 to 5 billion years, but they doubt it will develop such a tail because it is not moving through space as quickly.

'PHOENIX-LIKE REVIVALS'

"It's giving us this fantastic insight into the death processes of stars and their renewals -- their phoenix-like revivals as their ashes get cycled backed into the next generation of stars," added Michael Shara of the American Museum of Natural History and Columbia University in New York.

Shara said he expects that as this telescope continues mapping the cosmos in ultraviolet light for the first time, other similar stars may be discovered. "There must be lots more of these things," Shara said.

NASA images show the tail as a glowing light-blue stream of material including oxygen, carbon and nitrogen.

This material has been blown off Mira gradually over time -- the oldest was released roughly 30,000 years ago as part of a long stellar death process -- and is enough to form at least 3,000 future Earth-sized planets, the scientists said.

The astronomers were surprised to find this unique feature in Mira, a well-known star studied since the 16th century. Mira (pronounced MY-rah) stems from the Latin word for "wonderful."

Despite having about the same mass as the sun, Mira has swollen up to over 400 times the size of the sun, meaning the force of gravity is having a hard time holding it together, Seibert said.

The tail stretching 13 light-years is thousands of times the length of our solar system. The nearest star to Earth, called Proxima Centauri, is located 4 light-years away.

While this star looks like a comet, stars and comets are quite different celestial bodies. Comets in our solar system are relatively small objects made up of rock, dust and ice trailed by a tail of gas and dust.

Unlike our solitary sun, Mira is a so-called binary star traveling through space orbiting a companion believed to be the burnt-out, dead core of a star, known as a white dwarf.

Scientists think Mira in time will eject all its gas, leaving a colorful shell known as a planetary nebula that also gradually will fade leaving behind a white dwarf.

Astronomers surprised by star with comet-like tail | Science | Reuters