Astronomy Now Online
Home Magazine Resources Store


Top Stories


Milky Way a swifter spinner and more massive

...New suggest that our home Galaxy is spinning a dizzy 100,000 miles per hour faster than previously believed...

read more

Fermi unveils a dozen new pulsars

...NASA's Fermi Gamma-ray Space Telescope has discovered 12 new gamma-ray-only pulsars and has detected gamma-ray pulses from 18 others...

read more

Active galaxies vary across the Universe

...NASA’s Swift spacecraft is revealing that nearby active galaxies are more alive than those located halfway across the Universe...

read more



Spaceflight Now +



Subscribe to Spaceflight Now Plus for access to our extensive video collections!
How do I sign up?
Video archive

STS-120 day 2 highlights

Flight Day 2 of Discovery's mission focused on heat shield inspections. This movie shows the day's highlights.

 Play

STS-120 day 1 highlights

The highlights from shuttle Discovery's launch day are packaged into this movie.

 Play

STS-118: Highlights

The STS-118 crew, including Barbara Morgan, narrates its mission highlights film and answers questions in this post-flight presentation.

 Full presentation
 Mission film

STS-120: Rollout to pad

Space shuttle Discovery rolls out of the Vehicle Assembly Building and travels to launch pad 39A for its STS-120 mission.

 Play

Dawn leaves Earth

NASA's Dawn space probe launches aboard a Delta 2-Heavy rocket from Cape Canaveral to explore two worlds in the asteroid belt.

 Full coverage

Dawn: Launch preview

These briefings preview the launch and science objectives of NASA's Dawn asteroid orbiter.

 Launch | Science

Become a subscriber
More video



Hubble catches ballistic stars

BY DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 08 January, 2009

NASA's Hubble Space Telescope has captured 14 young, runaway stars slicing through regions of dense interstellar gas, creating brilliant bow shocks and leaving glowing tendrils in their wake.

"We think we have found a new class of bright, high-velocity stellar interlopers," says astronomer Raghvendra Sahai of NASA's Jet Propulsion Laboratory, and leader of the study. The team were using Hubble to search for long-lived pre-planetary nebula, swelling aging stars on the cusps of expelling their outer layers to become glowing nebulae. But instead they stumbled upon these youthful stellar runaways. "Finding these stars is a complete surprise because we were not looking for them. When I first saw the images, I said 'Wow. This is like a bullet speeding through the interstellar medium.' Hubble's sharp 'eye' reveals the structure and shape of these bow shocks."

Stellar interlopers caught speeding through space. Bright shocks can be seen as the stars' stellar winds collide with the dense surrounding gas. Image: NASA, ESA, and R. Sahai (NASA's Jet Propulsion Laboratory).

The bow shocks result from the stars' powerful stellar winds –streams of matter flowing from the stars – slamming into the surrounding dense gas. Depending on their distance from Earth, these bow shocks could be the equivalent of 17 to 170 Solar System diameters wide, as measured out to Neptune's orbit. The bow shocks can be used as a speed gauge, and indicate that the stars are whipping through space at more than 180,000 kilometers an hour with respect to the gas they are ploughing through, which is roughly five times faster than typical young stars. Their strong stellar winds combined with observations of the stars’ masses – they are medium sized stars up to eight times the Sun’s mass – indicates they are only a few million years old. Putting all this data together suggests that the stars could have covered a distance of about 160 light years (1.51 x 10^15 kilometres).

"The high-speed stars were likely kicked out of their homes, which were probably massive star clusters," says Sahai. This could have happened if one star in a binary system exploded as a supernova, kicking the companion star out of its gravitational grasp. Another scenario could have seen a collision between two binary star systems or a binary system and a third star. One or more of these stars could have gained enough energy from the interaction to escape the cluster.

This isn’t the first time that runaway stars have been seen running amok through the Universe. The Infrared Astronomical Satellite (IRAS), which performed an all-sky infrared survey in 1983, spied similar-looking objects but with much larger bow shocks than the stars in the Hubble study, suggesting that they are more massive stars with more powerful stellar winds.

"The stars in our study are likely the lower-mass and/or lower-speed counterparts to the massive stars with bow shocks detected by IRAS," Sahai explains. "We think the massive runaway stars observed before were just the tip of the iceberg. The stars seen with Hubble may represent the bulk of the population, both because many more lower-mass stars inhabit the Universe than higher-mass stars, and because a much larger number are subject to modest speed kicks."

The team is planning to probe selected objects from this survey in greater detail to understand their effects on their environment. "One of the questions that these very showy encounters raise is what effect they have on the clouds," says team member Mark Morris of the University of California, Los Angeles. "Is it an insignificant flash in the pan, or do the strong winds from these stars stir up the clouds and thereby slow down their evolution toward forming another generation of stars?"

The team also plans to build up the database with more interstellar interlopers, but the first challenge will be to track these runaways down; so far all of the known examples have been identified serendipitously.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
 GET YOUR COPY

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
 GET YOUR COPY

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
 GET YOUR COPY


HOME | NEWS ARCHIVE | MAGAZINE | SOLAR SYSTEM | SKY CHART | RESOURCES | STORE | SPACEFLIGHT NOW

© 2014 Pole Star Publications Ltd.