Published time: May 30, 2014
Milky Way, Andromeda galaxies set to collide
in giant game of space bumper cars
Andromeda galaxy will collide with Milky Way
은하우주와 안드로메다, M31 우주의 충돌, 37.5억년 후/
Milky Way galaxy and Andromeda galaxy are predicted to distort each other with tidal pull in 3.75 billion years/
은하우주와 안드로메다, M31 우주의 충돌, 37.5억년 후/
우리 은하와 안드로메다, m31 은하의 충돌 경로
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NASA astronomers say 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.
"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," says Sangmo Tony Sohn of the Space Telescope Science Institute (STScI) in Baltimore.
"Our findings are statistically consistent with a head-on collision between the Andromeda galaxy and our Milky Way galaxy," adds Roeland van der Marel of the STScI.
The Milky Way and Andromeda are moving toward each other under the inexorable pull of gravity. 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)
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.
The scenario is like a baseball batter watching an oncoming fastball. Although Andromeda is approaching us more than 2,000 times faster than a fastball, 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.
This series of photo illustrations shows the predicted merger between the Milky Way and Andromeda as seen from Earth. The first frame is the present day; the last frame is 7 billion years from now.
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.
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," says 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," adds 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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The Andromeda spiral galaxy. (Reuters/NASA)
우리 은하계, 안드로메다은하와 충돌 후 합병될 것
과학자들은 허블 우주망원경을 이용해 안드로메다의 영역별 접근 속도와 운동 양상을 관측한 결과 약 37억5천만년 후 두 은하가 충돌, 우리 은하계, 안드로메다의 거리는 약 200만 광년, 안드로메다은하가 우리은하에 접근하는 속도는 초속 100㎞ 이상. 두 우주 접근 속도 190만 km/hour(120만 mile/ hour, 약 20 억년, 10 억년후 상호 접촉시작 ...
이 속도로 두 은하가 접근한다면 앞으로 약 37.5억년 후에는 서로 충돌하게 될 것이다. 우리가 전혀 예측할 수 없는 수십 억년 후의 일이긴 하지만, 충돌할 경우 우리은하계에 어떠한 생명체도 존재하기 힘들어질지 모른다.
밀키 은하계, 안드로메다은하와 충돌 후 합병, 상상도
2012년 5월 31일자 사이언스 데일리(science daily) 웹사이트는, 미 항공우주국(NASA)의 한 천문학자가 "우리 은하계와 인접한 안드로메다(Andromeda) 은하계가 틀림없이 충돌해 합병될 것"으로 예측했다고 보도했다. 그 과정에서 우리 은하계와 태양계는 장차 거대한 변화가 발생할 것이다. 태양계는 은하계 중 새로운 구역으로 내던져지게 되겠지만 지구와 태양계가 소멸되지는 않을 것으로 보인다.
볼티모어 우주망원경 과학연구소(STSCI)의 롤란드 반더 마렐(Roeland Van der Marel)은 "우리의 연구 결과에 따르면 통계학적으로 안드로메다은하가 우리 은하계와 반드시 충돌할 것으로 나타났다"고 말했다. 천문학자들은 허블 우주망원경으로 많은 노력을 하여 안드로메다 은하계를 세밀히 측정했다. 안드로메다 은하계는 현재 250만 광년의 거리에 위치해 있는데 두 은하계의 상호 작용으로 불가피하게 점점 가까워지고 있다.
STSCI의 상모 토니 숀(Sangmo Tony Sohn)은 "최근 1세기 동안 안드로메다 은하계와 우리의 은하계에 대한 운명을 정밀하게 예측한바 우리는 미래에 확실히 충돌이 일어날 것으로 결론 내렸다"고 밝혔다. 이 장면은 마치 강속구가 야구방망이 정면을 향해 날아오는 것과 유사하다. 그러나 안드로메다의 접근 속도는 강속구에 비해 2천배 정도 빠르다. 비록 두 은하계가 서로 충돌해 합병되더라도, 각 은하계 내의 항성(恆星)들은 서로의 거리가 매우 멀어 그 과정에서 항성의 직접적인 충돌은 일어나지 않을 것으로 보인다. 그러나 성체(星體)들은 은하계 내에서 다른 궤도에 놓이게 될 것이다. 시뮬레이션 결과 태양계는 은하계 중심에서 거리가 멀리 떨어진 위치로 내던져질 것으로 나타났다.
더욱 복잡한 것은 M31(안드로메다)의 동반 은하계인 삼각형자리 은하 M33이 충돌되어 합병되는 과정에서 합류한다는 것이다. 1세기 전 천문학자들은 M31이 단독 은하계임을 알지 못했다. 에드윈 허블(Edwin Hubble)이 최초로 변광성(變星) 좌표를 이용해 거리를 측정해 M31 은하의 성체가 우리 은하계 범위를 아주 멀리 벗어나 있음을 확인했다. 그 뒤 M31이 시속 25만 마일(40만 km)의 속도로 우리 은하계 쪽으로 이동하고 있음을 측정해 냈다.
지금까지는 이런 상호작용으로 충돌이 일어날지는 알 수 없었다. 그러나 이번 관측으로 M31이 급격히 이동하고 있다는 결론을 내렸다. 이번 관측 전에 천문학자들은 M31의 고유운동을 충분히 측정할 수 없었다. 반더 마렐이 이끌고 있는 허블 우주망원경 팀은 M31의 고유운동을 정확히 측량하여 M31이 우리 은하계와 충돌해 병합될 것임을 확인했다. STSCI의 제이 앤더슨(Jay Anderson)은 "지난 5~7년 동안 은하계 내 선택지역을 반복적으로 관찰하여 시뮬레이션을 완성했다"고 했다. 시뮬레이션에서 나타난 최악의 시나리오는 은하계의 충돌로 별들이 각기 다른 궤도로 뿔뿔이 흩어지는 상황으로, 두 은하계가 균일한 팬케이크 모양의 원반 형상을 잃어버리고 타원형의 은하계를 형성하는 것이다.
참고자료: http://www.sciencedaily.com/releases/2012/05/120531135438.htm
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NASA, Physics, SciTech, Science, Space, USA
A short time ago, in a galaxy very, very close by, a NASA satellite thought it detected a gamma ray burst in Andromeda. It was a false alarm, but astronomers used the opportunity as a reminder that our galaxy and Andromeda are set for a head-on collision.
NASA’s Swift satellite discovers and measures gamma-ray bursts, the most powerful explosions in the universe, and their afterglow in X-ray, optical, and ultraviolet wavelengths of light. The space agency says the spacecraft is designed “with powerful telescopes and quick reflexes to capture gamma-ray bursts as they flash and leave a lingering afterglow.”
On Wednesday, astronomers and astrophiles alike buzzed with the news that Swift’s equipment had captured a powerful flash of gamma rays, believed to be coming from the Andromeda Galaxy. Those who watch the sky were caught up in the possibility that a clashing pair of neutron stars or a bright X-ray source was acting up a mere 2.5 million light-years away, NBC News reported.
But, alas, the excitement was short-lived. By the time more raw data came in and the initial information was re-analyzed, the project team realized what they thought was a giant burst of radiation was not the dense remnants of dead stars crashing together.
“We... do not believe this source to be in outburst. Instead, it was a serendipitous constant source in the field of view of a BAT subthreshold trigger,” Swift team member Kim Page wrote in a NASA message.
The reason scientists (and the Twittersphere) were in such a tizzy was because, “The Andromeda galaxy, known in astronomical parlance as M31, holds a special place in our own future,” the New York Times wrote.
NASA astronomers announced in 2012 “with certainty” that the next major cosmic event to hit the Milky Way will quite literally hit the Milky Way. Our galaxy will have a “titanic collision” with neighboring Andromeda. Not only that, the Triangulum galaxy, M33, is likely to join in on the action, causing a three-galaxy pile-up (and could even merge with the other two), scientists said in a statement.
The Milky Way and Andromeda are the dominant members of a small family of galaxies called the Local Group. Family ties bind the bevy together in the form of their mutual gravity.
NASA sought to assure the world that the sun and Earth are unlikely to be hit by stars or planets from Andromeda because of the vast emptiness of the two galaxies.
So Earth, they said, should easily survive what will be a 1.9 million kilometer per hour (1.2 million mile per hour) galactic merger. Even at that speed, the event would take about 2 billion years.
"It's like a bad car crash in galaxy-land," Roeland van der Marel, an astronomer with the Space Telescope Science Institute in Baltimore, which operates Hubble, told the media.
Scientists said in 2012 the collision would take place in 4 billion years. But the New York Times reported Wednesday, “Recent measurements with the Hubble Space Telescope have confirmed that they will hit head on in about two billion years.” Apparently the galaxies have gone to “ludicrous speed,” as the movie Spaceballs would say. One can only hope the light show from the combined galaxies won’t be plaid.