New Delhi: According to modern cosmology, galaxies evolve through a graded process of colliding with and merging with other systems. Our own galaxy, which is 13.61 billion years old, provides the clearest view of this formation.
A team of astronomers from the Harvard-Smithsonian Center for Astrophysics (CFA) recently tried to piece together the history of the Milky Way’s stars in unprecedented detail to determine the nature of the Milky Way’s eventual merger.
Their findings were recently published in The Astrophysical Journal.
Currently, two nearby dwarf galaxies, the Large and Small Magellanic Clouds, are falling towards us. The Large and Small Magellanic Clouds account for about one percent and 0.7 percent, respectively, of the Milky Way’s stellar mass.
In addition, currents from globular clusters circle the Milky Way, and this marks the effects of a prior merger.
Astronomers access data from Gaia spacecraft
CFA astronomers used results from the Gaia spacecraft, which was launched in 2013, to conduct the study, surveying one percent of its nearly 100 billion stars to produce an accurate three-dimensional map of the Milky Way. with target.
Astronomers combined the Gaia results with a new survey (the H3 Survey of the Stars) of our galaxy’s outer reaches with the 6.5-meter MMT telescope in Arizona.
A dwarf galaxy merged with the Milky Way in the past
A single dwarf galaxy known as Gaia-Sausage-Enceladus (GSE) merged with the Milky Way some eight to ten billion years ago. The stellar motions and compositions of the stars in GSE’s inner halo help scientists estimate what’s left of the object.
However, it is not certain whether the GSE encountered the Milky Way, or whether it orbited the Milky Way before slowly merging.
To answer these questions, astronomers combined the measured halo stars of Gaia with a set of numerical simulations comparing stellar ages and compositions.
The researchers observed that the GSE contained about half a billion stars, and did not orbit the Milky Way, but instead approached in a retrograde direction, meaning that it approached the Milky Way in the opposite direction to the Milky Way’s rotational motion. .
Half of the stars in the Milky Way are descended from dwarf galaxies
They concluded that about 50 percent of the Milky Way’s current stellar halo, and about 20 percent of its dark matter halo, descended from a dwarf galaxy called GSE. The stellar halo of the Milky Way is a spherical distribution of stars, approximately one million light-years in diameter, and about 10 to 12 billion years old.
Some of the stars in the Milky Way are about 13 billion years old, and may have been captured by the Milky Way after it formed.
The completion of the research will help scientists trace nearly the entire evolution of the Milky Way over the past 10 billion years.
Some galaxies are moving towards the Milky Way
The Small Magellanic Cloud is a nearby dwarf galaxy found in the Milky Way, the study said.
In addition, a neighbor of the Milky Way, the Sagittarius Dwarf Galaxy, is undergoing tidal disruption (an astronomical phenomenon in which a star approaches a supermassive black hole and is torn apart by the black hole’s tidal force).
Records of ancient mergers can be derived from the positions and motions of stars in the Milky Way’s stellar halo.
The Andromeda Galaxy, our largest neighbor galaxy, is about ten times farther than dwarf galaxies. The merger of the Milky Way and Andromeda is expected in the next five billion years.
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