Milchstraße:Kollision mit Andromeda – Neues aus dem All

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Milchstraße:Kollision mit Andromeda

Das Schicksal unserer Heimatgalaxie ist besiegelt: Die Milchstraße wird mit der benachbarten Andromeda-Galaxie zusammenstoßen und dabei völlig umgekrempelt – allerdings erst in vier Milliarden Jahren. Über entsprechende Messungen des Weltraumteleskops “Hubble” berichtete die Nasa in Washington.

“Nach fast einem Jahrhundert Spekulationen über das Schicksal der Andromeda-Galaxie und unserer Milchstraße haben wir endlich ein klares Bild davon, was während der kommenden Milliarden Jahre passieren wird”, so das Space Telescope Science Institute Baltimore.

“Schwarze Venus” vor der Sonne

Ein seltenes Himmelsschauspiel ist am kommenden Mittwoch (6.Juni) zu sehen: Die “Schwarze Venus” wird sich vor die Sonne schieben. Bei wolkenfreiem Wetter können Astronomie-Fans beobachten, wie unser Nachbarplanet Venus von der Erde aus gesehen als kleiner schwarzer Punkt westwärts über die Sonnenscheibe wandert. Astronomen bezeichnen diese Mini-Sonnenfinsternis als Venustransit.

Erst 2117 wird es wieder eine solche Konstellation geben. Bislang wurden in der Geschichte der Astronomie erst sechs Venusdurchgänge beobachtet: 1639, 1761, 1769, 1874, 1882 und 2004.

Mars-Methan stammt von Meteoriten

Das Methan auf dem Mars stammt nach einer Studie zu einem großen Teil aus Meteoriten – und demnach eher nicht von Lebewesen. Das entdeckten Forscher des Max-Planck-Instituts für Chemie in Mainz gemeinsam mit Kollegen aus den Niederlanden und Großbritannien.

Für viele Experten galten die vor neun Jahren entdeckten Methan-Vorkommen in der Atmosphäre des unwirtlichen Planeten als Hinweis auf außerirdisches Leben. Das Team hatte Teile eines Meteoriten unter Mars-Bedingungen mit ultraviolettem Licht bestrahlt, woraufhin sich Methan bildete.

Alter der äußeren Milchstraße klar

Das Alter der äußeren Milchstraße ist mit einer neuen Analyse genau bestimmt worden. Der sogenannte innere Halo unserer Galaxis ist demnach etwa 11,4 Milliarden Jahre alt. Das schließt Jason Kalirai vom Space Telescope Science Institute in Baltimore (USA) aus der Untersuchung Weißer Zwergsterne, wie er im britischen Fachjournal “Nature” erläutert.

Als galaktischen Halo bezeichnen Astronomen die Ansammlung von Sternen und Kugelsternhaufen, die wie eine gigantische Kugel um die flache galaktische Scheibe unserer Galaxie verteilt sind.


Hier der Beitrag in Englisch:

Collision Scenario for Milky Way and Andromeda Galaxy Encounter


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 four 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 team member 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.”

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.

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