Setting the Galaxy's Age : Discovery News
12-07-08 11:22 AM
skip to main content
earth
space
tech and gadgets
animals
history
adventure
human
brain games
video
rss feeds
discovery.com
Discovery News > Space News > Setting the Galaxy's Age
Setting the Galaxy's Age
A scientist cracks the code using white dwarf stars to determine when
the Milky Way got its halo.
http://news.discovery.com/space/milky-way-age-120530.html
Page 1 of 10
Setting the Galaxy's Age : Discovery News
12-07-08 11:22 AM
By Irene Klotz
Wed May 30, 2012 01:24 PM ET
(1) Comments | Leave a Comment
Print
Email
Friend's Name:
Email:
Your Name:
Email:
Message:
characters left = 100
submit reset
close
42 people like this. Be the first of your
friends.
Like
Tweet
79
THE GIST
New technique shows Milky Way’s halo is 11.4 billion years old.
The halo is believed to be the oldest structure of the galaxy.
An astronomer used fresh stellar corpses, so-called white dwarf stars, to determine the halo's age.
enlarge
An ingenious way of measuring the ages of stellar populations in the halo of the Milky Way will allow astronomers to
obtain direct information on the timing of the Galaxy's evolution. Click to enlarge this image.
http://news.discovery.com/space/milky-way-age-120530.html
Page 2 of 10
Setting the Galaxy's Age : Discovery News
12-07-08 11:22 AM
Ivan Eder/NASA
Scientists trying to piece together the story of how the universe evolved from clumps of dark matter into the sparkling
galaxies of today have had to work around a central problem -- no reliable technique to determine the age of small
stars like the sun, which are the most common.
An astronomer at the Space Telescope Science Institute has taken a big step in resolving the puzzle. Jason Kalirai used
fresh stellar corpses of sun-like stars to serve as a key to time.
PHOTOS: Top Exoplanets For Alien Life
“It’s like putting hands on a clock,” Timothy Beers, director of Kitt Peak National Observatory, told Discovery News.
By analyzing four of these newly dead stars, Kalirai determined that the inner halo of stars surrounding the Milky
Way is 11.4 billion years old.
The halo is spherical cloud of objects that are not orderly rotating around
the center of the galaxy, like the sun and other stars in the Milky Way’s
disk do.
“You’re either rotating around the center in an organized fashion -- that’s
the disk -- or you’re supported by rapid, random motions. That’s the
halo,” Beers said.
Within the halo are at least two populations of stars, again characterized
less by location and more by relative motion.
How the stars came to be part of the Milky Way remains a mystery, but
Kalirai’s technique can be used to home in on when they arrived.
WATCH VIDEO: Findings bolster the
argument that Dark Energy is the
reason our universe is expanding.
“When an object comes into the halo, it gets shredded from its parent galaxy and depending on what the orbit was of
that parent galaxy it is going to be moving in that orientation. By knowing when those stars formed, we have a limit
on when they were accreted into the Milky Way because they couldn’t have been accreted before they were formed,“
Kalirai told Discovery News.
“Until this came along there was really no good way to quantify the age of the stellar distribution,” Beers added.
“Jason takes a handful of a set of stars, believed to be part of the inner halo population, age them and assigns them to a
population from which they were drawn,” said Beers, who called the approach “ingenious.”
Kalirai chose so-called white dwarf stars as his portholes because they are simple stars whose light can be broken
down into composite wavelengths impregnated with features directly relating to the star’s properties, such as its mass
and temperature.
“You can measure it in a straightforward way. You can’t do that for normal hydrogen-burning stars,” Kalirai said.
White dwarfs are what remain after sun-like stars burn through all their hydrogen and shed their outer layers. They are
1 million times more dense than anything on Earth.
“If you took a tablespoon of material from the surface of a white dwarf, it would weigh as much as a school bus here
on Earth,” Kalirai said.
They are also terribly common in the Milky Way. About 98 percent of the stars in the galaxy will end their lives as
http://news.discovery.com/space/milky-way-age-120530.html
Page 3 of 10
Setting the Galaxy's Age : Discovery News
12-07-08 11:22 AM
white dwarfs.
NEWS: Milky Way’s Gamma-Ray Bubbles Shaped By Dark Matter?
Kalirai picked the newest corpses, ones uncomplicated by cooling, to resurrect key details of the stars they once were,
such as their mass and temperature, then used that information to determine their age.
The next step is to find similar stars in the outer halo population, which is believed to contain objects that predate the
Milky Way itself. Astronomers suspect some so-called globular clusters -- massive, densely packed clusters of stars -are remnants of smaller proto-galaxies axed by gravity and reassembled into building blocks for the Milky Way.
“Galaxies don’t just collapse as one big ball. They get assembled from many smaller pieces that become larger as they
interact with each other,” Beers said.
“How and when they do it is exactly the story we want to tell, “ he added.
“This technique enables us to make meaningful comparisons between the stellar populations of the halo. One can then
work out a timeline for the assembly of the galaxy,” Beers said.
Kalirai’s research appears today on Nature's website.
Tags: Dark Energy, Dark Matter, Galaxies, Life, Science
Like
Tweet
42 people like this. Be the first of your friends.
79
10
stumbleupon share
digg share
reddit share
NEXT STORY: Ready for the Last Venus Transit Until 2117? next
YOU MIGHT ALSO LIKE
Milky Way's
Gamma-ray Bubbles
Shaped by Dark
Matter?
Shrunken Head
DNA Proves
Horrific Folklore
True
http://news.discovery.com/space/milky-way-age-120530.html
Top 10 Reasons
Why the World
Won't End in 2012
Milky Way Doomed
to Crash with
Andromeda
Page 4 of 10