Next Major Cosmic Event in 4 Billion Years - Milky Way

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NASA's Hubble Shows Milky Way is Destined for Head-On Collision

05.31.12

 

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.

This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth's night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. (Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger)
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"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.

This animation depicts the collision between our Milky Way galaxy and the Andromeda galaxy. Hubble Space Telescope observations indicate that the two galaxies, pulled together by their mutual gravity, will crash together about 4 billion years from now. Around 6 billion years from now, the two galaxies will merge to form a single galaxy. The video also shows the Triangulum galaxy, which will join in the collision and perhaps later merge with the Andromeda/Milky Way pair. (Visualization Credit: NASA; ESA; and F. Summers, STScI | Simulation Credit: NASA; ESA; G. Besla, Columbia University; and R. van der Marel, STScI) › Download video (45 MB mp4) › Download video (no annotations)

"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 2,000 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.

This illustration shows the collision paths of our Milky Way galaxy and the Andromeda galaxy. The galaxies are moving toward each other under the inexorable pull of gravity between them. Also shown is a smaller galaxy, Triangulum, which may be part of the smashup. (Credit: NASA; ESA; A. Feild and R. van der Marel, STScI)
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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, N.Y. "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."

This series of photo illustrations shows the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy.

• First Row, Left: Present day.
• First Row, Right: In 2 billion years the disk of the approaching Andromeda galaxy is noticeably larger.
• Second Row, Left: In 3.75 billion years Andromeda fills the field of view.
• Second Row, Right: In 3.85 billion years the sky is ablaze with new star formation.
• Third Row, Left: In 3.9 billion years, star formation continues.
• Third Row, Right: In 4 billion years Andromeda is tidally stretched and the Milky Way becomes warped.
• Fourth Row, Left: In 5.1 billion years the cores of the Milky Way and Andromeda appear as a pair of bright lobes.
• Fourth Row, Right: In 7 billion years the merged galaxies form a huge elliptical galaxy, its bright core dominating the nighttime sky.

(Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas, and A. Mellinger)
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The space shuttle servicing missions to Hubble upgraded it with ever more-powerful cameras, which have given astronomers a long-enough time baseline to make the critical measurements needed to nail down M31's motion. The Hubble observations and the consequences of the merger are reported in three papers that will appear in an upcoming issue of the Astrophysical Journal.

For more images, video and information about M31's collision with the Milky Way, visit:http://hubblesite.org/news/2012/20

Black Hole Ejected from Host Galaxy

June 4, 2012

J.D. Harrington 
Headquarters, Washington 
202-358-5241 
j.d.harrington@nasa.gov 

Megan Watzke 
Chandra X-ray Center, Cambridge, Mass. 
617-496-7998 
mwatzke@cfa.harvard.edu 

RELEASE: 12-182

GIANT BLACK HOLE KICKED OUT OF HOME GALAXY

WASHINGTON -- Astronomers have found strong evidence that a massive 
black hole is being ejected from its host galaxy at a speed of 
several million miles per hour. New observations from NASA's Chandra 
X-ray Observatory suggest that the black hole collided and merged 
with another black hole and received a powerful recoil kick from 
gravitational wave radiation. 

"It's hard to believe that a supermassive black hole weighing millions 
of times the mass of the sun could be moved at all, let alone kicked 
out of a galaxy at enormous speed," said Francesca Civano of the 
Harvard-Smithsonian Center for Astrophysics (CfA), who led the new 
study. "But these new data support the idea that gravitational waves 
-- ripples in the fabric of space first predicted by Albert Einstein 
but never detected directly -- can exert an extremely powerful 
force." 

Although the ejection of a supermassive black hole from a galaxy by 
recoil because more gravitational waves are being emitted in one 
direction than another is likely to be rare, it nevertheless could 
mean that there are many giant black holes roaming undetected out in 
the vast spaces between galaxies. 

"These black holes would be invisible to us," said co-author Laura 
Blecha, also of CfA, "because they have consumed all of the gas 
surrounding them after being thrown out of their home galaxy." 

Civano and her group have been studying a system known as CID-42, 
located in the middle of a galaxy about 4 billion light years away. 
They had previously spotted two distinct, compact sources of optical 
light in CID-42, using NASA's Hubble Space Telescope. 

More optical data from the ground-based Magellan and Very Large 
Telescopes in Chile supplied a spectrum (that is, the distribution of 
optical light with energy) that suggested the two sources in CID-42 
are moving apart at a speed of at least 3 million miles per hour. 

Previous Chandra observations detected a bright X-ray source likely 
caused by super-heated material around one or more supermassive black 
holes. However, they could not distinguish whether the X-rays came 
from one or both of the optical sources because Chandra was not 
pointed directly at CID-42, giving an X-ray source that was less 
sharp than usual. 

"The previous data told us that there was something special going on, 
but we couldn't tell if there were two black holes or just one," said 
another co-author Martin Elvis, also of CfA. "We needed new X-ray 
data to separate the sources." 

When Chandra's sharp High Resolution Camera was pointed directly at 
CID-42, the resulting data showed that X-rays were coming only from 
one of the sources. The team thinks that when two galaxies collided, 
the supermassive black holes in the center of each galaxy also 
collided. The two black holes then merged to form a single black hole 
that recoiled from gravitational waves produced by the collision, 
which gave the newly merged black hole a sufficiently large kick for 
it to eventually escape from the galaxy. 

The other optical source is thought to be the bright star cluster that 
was left behind. This picture is consistent with recent computer 
simulations of merging black holes, which show that merged black 
holes can receive powerful kicks from the emission of gravitational 
waves. 

There are two other possible explanations for what is happening in 
CID-42. One would involve an encounter between three supermassive 
black holes, resulting in the lightest one being ejected. Another 
idea is that CID-42 contains two supermassive black holes spiraling 
toward one another, rather than one moving quickly away. 

Both of these alternate explanations would require at least one of the 
supermassive black holes to be very obscured, since only one bright 
X-ray source is observed. Thus the Chandra data support the idea of a 
black hole recoiling because of gravitational waves. 

These results will appear in the June 10 issue of The Astrophysical 
Journal. 

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the 
Chandra Program for the agency's Science Mission Directorate in 
Washington. The Smithsonian Astrophysical Observatory in Cambridge, 
Mass., controls Chandra's science and flight operations. 

For Chandra images, multimedia and related materials, visit: 

http://www.nasa.gov/chandra 

For an additional interactive image, podcast, and video on the 
finding, visit: 

http://chandra.si.edu 

 
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