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Scientists: Milky Way Merged with Another Smaller Galaxy Roughly 10 Billion Years Ago

The Milky Way, home to our sun and billions of other stars, merged with another smaller galaxy in a colossal cosmic collision roughly 10 billion years ago

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Milky Way, Galaxy, Scientists
FILE - A view of the Milky Way from an area of Puyehue National Park near Osorno City, Chile, May 8, 2008. VOA

The Milky Way, home to our sun and billions of other stars, merged with another smaller galaxy in a colossal cosmic collision roughly 10 billion years ago, scientists said Monday, based on data from the Gaia space observatory.

The union of the Milky Way and the so-called dwarf galaxy Gaia-Enceladus increased our galaxy’s mass by about a quarter and triggered a period of accelerated star formation lasting about 2 to 4 billion years, the scientists said.

“Yes, indeed it was a pivotal moment,” said astronomer Carme Gallart of Instituto de Astrofisica de Canarias in Spain, lead author of the research published in the journal Nature Astronomy.

Galaxies of all types including the Milky Way began to form relatively soon after the Big Bang explosion that marked the beginning of the universe some 13.8 billion years ago, but were generally smaller than those seen today and were forming stars at a rapid rate. Subsequent galactic mergers were instrumental in configuring galaxies existing now.

Milky Way, Galaxy, Scientists
The merger of the Milky Way and the dwarf galaxy Gaia-Enceladus roughly 10 billion years ago, left, and the current appearance of the Milky Way galaxy, right, are shown in this artist’s conception, July 22, 2019. VOA

High-precision measurements of the position, brightness and distance of around a million stars within 6,500 light years of the sun, obtained by the Gaia space telescope operated by the European Space Agency, helped pinpoint stars present before the merger and those that formed afterward.

Certain stars with higher content of elements other than hydrogen or helium arose in the Milky Way, they found, and others with lower such content originated in Gaia-Enceladus, owing to its smaller mass.

While the merger was dramatic and helped shape what the Milky Way has become, it was not a star-destroying calamity.

“This crash was big in cosmic terms, but if it was happening now, we could probably not even notice at a human or solar system level,” Gallart said.

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“The distances between stars in a galaxy are so huge — a galaxy is basically empty space — that the two galaxies intermix, change their global shape, more star formation may happen in one, and maybe the small one stops forming stars.

“But the individual stars in each galaxy don’t collide, don’t really notice the force of the event in a way that affects their individual evolution or the evolution of the planetary systems that may be attached to them,” Gallart said.

The Milky Way, spiral shaped with a central bar-like structure composed of stars, includes 100 to 400 billion stars, including the sun, which formed roughly 4.5 billion years ago, far after the merger. (VOA)

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Chinese Researchers Spot Monster Black Hole Bigger Than Sun

Chinese team spots monster black hole which is 70 times bigger than Sun

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Black Hole
A team of Chinese scientists spotted a black hole that is 70 times larger than the sun. (Representational Image Only). Wikimedia Commons

A team led by Chinese researchers has spotted a monster black hole with a mass 70 times greater than Sun — toppling the earlier assumption that the mass of an individual black hole in our Galaxy is no more than 20 times that of Sun.

Our Milky Way Galaxy is estimated to contain 100 million stellar black holes — cosmic bodies formed by the collapse of massive stars and so dense even light can’t escape.

The team, headed by Professor LIU Jifeng of the National Astronomical Observatory of China of the Chinese Academy of Sciences (NAOC), spotted a stellar black hole with a mass 70 times greater than the Sun.

The monster black hole is located 15 thousand light-years from Earth and has been named “LB-1” by the researchers in a paper reported in the journal Nature.

“Black holes of such mass should not even exist in our Galaxy, according to most of the current models of stellar evolution,” said LIU.

“We thought that very massive stars with the chemical composition typical of our Galaxy must shed most of their gas in powerful stellar winds, as they approach the end of their life. Therefore, they should not leave behind such a massive remnant,” he explained.

Spotting black hole
The monster black hole is located 15 thousand light-years from Earth. (Representational Image Only). Wikimedia Commons

Until just a few years ago, stellar black holes could only be discovered when they gobbled up gas from a companion star.

The vast majority of stellar black holes in our Galaxy are not engaged in a cosmic banquet, though, and thus don’t emit revealing X-rays.

As a result, only about two dozen Galactic stellar black holes have been well identified and measured.

To counter this limitation, LIU and collaborators surveyed the sky with China’s Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST).

After the initial discovery, the world’s largest optical telescopes – Spain’s 10.4-m Gran Telescopio Canarias and the 10-m Keck I telescope in the US – were used to determine the system’s physical parameters.
The results were nothing short of fantastic: a star eight times heavier than the Sun was seen orbiting a 70-solar-mass black hole, every 79 days.

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The direct sighting of LB-1 proves that this population of over-massive stellar black holes exists even in our own backyard.

“This discovery forces us to re-examine our models of how stellar-mass black holes form,” said LIGO Director Professor David Reitze from University of Florida in the US. (IANS)