For many years humans thought that they belong to one galaxy called the Milky Way. They have observed it through telescopes and were fascinated by many stars it consists of. But, along came a surprise: they weren't born into it.
If you are baffled, do not worry. Scientists were too when they realized that the Sun, the Moon, our planet and its siblings did not actually come from a Milky Way Galaxy but from a strange formation called the Sagittarius Dwarf Galaxy.
University of Massachusetts conducted a major project known as Two-Micron All Sky Survey (2MASS) which computed data of sky in infrared light. For decades scientists were confused about a huge part of "our" galaxy, when they finally realized that Milky Way is consuming one of its neighbours (galactic cannibalism).
The study was published in the Astrophysical Journal and it is the first study which mapped the full extent of the Sagittarius Galaxy, showing in great detail how its debris wraps around and passes right through Milky Way. Sagittarius is 10,000 times smaller than the galaxy the Earth belongs to now and thus, it is getting stretched out, torn apart and gobbled by the bigger Milky Way.
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The Project
This survey was conducted back in 2003 and it used a supercomputer to sort through half a billion stars to create the so-called NEW STAR MAP to basically show the Solar System right on the crossroads where two galaxies are actually joining.
"It's clear who's the bully in the interaction," said Steven Majewski, U.Va. professor of astronomy and lead author on the paper describing the results. If people had infrared-sensitive eyes, the entrails of Sagittarius would be a prominent fixture sweeping across our sky. But at human, visual wavelengths, they become buried among countless intervening stars and obscuring dust. The great expanse of the Sagittarius system has been hidden from view."
However, this survey tried to isolate the most important stars and concentrate on a type of star called an M giant. These giants can be mostly found in the Sagittarius galaxy and they're really uncommon in the Milky Way. Majewski and his team were able to find these Sagittarius stars and show that the Milky Way is basically gobbling them. Before, astronomers were only able to find pieces of the disrupted Sagittarius dwarf.
Here's an animation of the "Marriage" between the two:
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(I also suggest watching animated movies of
marriage and
strange behaviour).
For decades, astronomers were puzzled about why the Milky Way is at an angle. The theory behind their thinking was that if our planet really did originate from the Milky Way we would be oriented to the galaxy's ecliptic, with all of the planets aligned around the Sun in the same angle as our Sun is aligned to the Milky Way. However, the angle suggests that our Sun is actually influenced by a completely different system. In conclusion, our galaxy is the Sagittarius Dwarf Galaxy and not Milky Way!
"We sifted several thousand interesting stars from a catalog of half a billion," said co-author Michael Skrutskie, U.Va. professor of astronomy and principal investigator for the 2MASS project. "By tuning our maps of the sky to the 'right' kind of star, the Sagittarius system jumped into view."This first full-sky map of Sagittarius shows its extensive interaction with the Milky Way. Both stars and star clusters now in the outer parts of the Milky Way have been 'stolen' from Sagittarius as the gravitational forces of the Milky Way nibbled away at its dwarf companion. This one vivid example shows that the Milky Way grows by eating its smaller neighbors."
Sagittarius has been playing this game with Milky Way for approximately 2 billion years and now it has reached that critical point and started dancing the "slow dance of death."
"After slow, continuous gnawing by the Milky Way, Sagittarius has been whittled down to the point that it cannot hold itself together much longer," said 2MASS Science Team member and study co-author Martin Weinberg of the University of Massachusetts. "We are seeing Sagittarius at the very end of its life as an intact system."
What is Actually Happening?
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"For only a few percent of its 240 million-year orbit around the Milky Way galaxy does our Solar System pass through the path of Sagittarius debris," Majewski said. "Remarkably, stars from Sagittarius are now raining down onto our present position in the Milky Way. Stars from an alien galaxy are relatively near us. We have to re-think our assumptions about the Milky Way galaxy to account for this contamination."
Thus, the Earth does not belong to Milky Way. Well, now it does but it was not born into it and its original galaxy is dying out slowly, while pieces of it are combining with the Milky Way Galaxy which today humans call home. So, say hello to Sagittarius and also say goodbye while you're at it.
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