Photo Credit: NASA
FROM: NASA
WASHINGTON -- NASA astronomers announced Thursday they can now predict
with certainty the next major cosmic event to affect our galaxy, sun,
and solar system: the titanic collision of our Milky Way galaxy with
the neighboring Andromeda galaxy.
The Milky Way is destined to get a major makeover during the
encounter, which is predicted to happen four billion years from now.
It is likely the sun will be flung into a new region of our galaxy,
but our Earth and solar system are in no danger of being destroyed.
"Our findings are statistically consistent with a head-on collision
between the Andromeda galaxy and our Milky Way galaxy," said Roeland
van der Marel of the Space Telescope Science Institute (STScI) in
Baltimore.
The solution came through painstaking NASA Hubble Space Telescope
measurements of the motion of Andromeda, which also is known as M31.
The galaxy is now 2.5 million light-years away, but it is inexorably
falling toward the Milky Way under the mutual pull of gravity between
the two galaxies and the invisible dark matter that surrounds them
both.
"After nearly a century of speculation about the future destiny of
Andromeda and our Milky Way, we at last have a clear picture of how
events will unfold over the coming billions of years," said Sangmo
Tony Sohn of STScI.
The scenario is like a baseball batter watching an oncoming fastball.
Although Andromeda is approaching us more than two thousand times
faster, it will take 4 billion years before the strike.
Computer simulations derived from Hubble's data show that it will take
an additional two billion years after the encounter for the
interacting galaxies to completely merge under the tug of gravity and
reshape into a single elliptical galaxy similar to the kind commonly
seen in the local universe.
Although the galaxies will plow into each other, stars inside each
galaxy are so far apart that they will not collide with other stars
during the encounter. However, the stars will be thrown into
different orbits around the new galactic center. Simulations show
that our solar system will probably be tossed much farther from the
galactic core than it is today.
To make matters more complicated, M31's small companion, the
Triangulum galaxy, M33, will join in the collision and perhaps later
merge with the M31/Milky Way pair. There is a small chance that M33
will hit the Milky Way first.
The universe is expanding and accelerating, and collisions between
galaxies in close proximity to each other still happen because they
are bound by the gravity of the dark matter surrounding them. The
Hubble Space Telescope's deep views of the universe show such
encounters between galaxies were more common in the past when the
universe was smaller.
A century ago astronomers did not realize that M31 was a separate
galaxy far beyond the stars of the Milky Way. Edwin Hubble measured
its vast distance by uncovering a variable star that served as a
"milepost marker."
Hubble went on to discover the expanding universe where galaxies are
rushing away from us, but it has long been known that M31 is moving
toward the Milky Way at about 250,000 miles per hour. That is fast
enough to travel from here to the moon in one hour. The measurement
was made using the Doppler effect, which is a change in frequency and
wavelength of waves produced by a moving source relative to an
observer, to measure how starlight in the galaxy has been compressed
by Andromeda's motion toward us.
Previously, it was unknown whether the far-future encounter will be a
miss, glancing blow, or head-on smashup. This depends on M31’s
tangential motion. Until now, astronomers had not been able to
measure M31's sideways motion in the sky, despite attempts dating
back more than a century. The Hubble Space Telescope team, led by van
der Marel, conducted extraordinarily precise observations of the
sideways motion of M31 that remove any doubt that it is destined to
collide and merge with the Milky Way.
"This was accomplished by repeatedly observing select regions of the
galaxy over a five- to seven-year period," said Jay Anderson of
STScI.
"In the worst-case-scenario simulation, M31 slams into the Milky Way
head-on and the stars are all scattered into different orbits," said
Gurtina Besla of Columbia University in New York. "The stellar
populations of both galaxies are jostled, and the Milky Way loses its
flattened pancake shape with most of the stars on nearly circular
orbits. The galaxies' cores merge, and the stars settle into
randomized orbits to create an elliptical-shaped galaxy."
Image credit: NASA/JPL-Caltech
FROM: NASA
The Galaxy Next Door
Hot stars burn brightly in this new image from NASA's Galaxy Evolution Explorer, showing the ultraviolet side of a familiar face.
At approximately 2.5 million light-years away, the Andromeda galaxy, or M31, is our Milky Way's largest galactic neighbor. The entire galaxy spans 260,000 light-years across -- a distance so large, it took 11 different image segments stitched together to produce this view of the galaxy next door.
The bands of blue-white making up the galaxy's striking rings are neighborhoods that harbor hot, young, massive stars. Dark blue-grey lanes of cooler dust show up starkly against these bright rings, tracing the regions where star formation is currently taking place in dense cloudy cocoons. Eventually, these dusty lanes will be blown away by strong stellar winds, as the forming stars ignite nuclear fusion in their cores. Meanwhile, the central orange-white ball reveals a congregation of cooler, old stars that formed long ago.
When observed in visible light, Andromeda’s rings look more like spiral arms. The ultraviolet view shows that these arms more closely resemble the ring-like structure previously observed in infrared wavelengths with NASA’s Spitzer Space Telescope. Astronomers using Spitzer interpreted these rings as evidence that the galaxy was involved in a direct collision with its neighbor, M32, more than 200 million years ago.
Andromeda is so bright and close to us that it is one of only ten galaxies that can be spotted from Earth with the naked eye. This view is two-color composite, where blue represents far-ultraviolet light, and orange is near-ultraviolet light.
