New analysis reveals that our quiet, middle-aged galaxy was once fairly the firecracker — a pair billion years in the past it was making new stars at 10 instances the speed it’s as we speak.
The Milky Manner is fairly sedate as galaxies go. It makes only a Solar’s value of stars a 12 months, when starburst galaxies might manufacture a whole bunch or hundreds of instances that fee. However the European House Company’s Gaia satellite tv for pc is offering a window into our galaxy’s previous, which reveals a really completely different view: Only a couple billions of years in the past, one thing ignited a stellar firestorm in our galaxy.
The Gaia mission launched a transformative catalog simply over a 12 months in the past, recording exact distance and movement measurements for greater than a billion stars in our galaxy. Now, Roger Mor (College of Barcelona, Spain) and colleagues are utilizing that beautiful information set, together with some subtle pc algorithms, to delve into the Milky Manner’s previous. Their outcomes seem in Astronomy & Astrophysics.
The researchers choose the obvious brightness, colour, and distance for two.9 million stars within the Gaia catalog. They then feed this data right into a simulation, which reconstructs each the preliminary stellar plenty — that’s, counting out what number of small stars fashioned relative to the few very huge ones — and the best way these stars are distributed within the galaxy.
By understanding how the celebs fashioned and the place they’re now, the simulation can recreate the galaxy’s star formation historical past. The outcomes are intriguing: About 10 billion years in the past, our younger galaxy was making stars by the handfuls. However its manufacturing fee was in regular decline for the subsequent 5 billion years. Certainly, earlier research have urged that the Milky Manner swallowed a Small Magellanic Cloud-size galaxy, dubbed Gaia-Enceladus, greater than 10 billion years in the past. That merger might need stimulated a rush of star formation earlier than finally quashing it.
Then, 5 billion years in the past, or maybe even earlier, one other occasion ignited a stellar child growth. The proliferation of recent stars lasted some four billion years. Maybe, the authors speculate, the Milky Manner had collided once more, this time with a gas-rich satellite tv for pc galaxy. That will clarify the lengthy growth, which peaked 1 or 2 billion years after it began, when stars had been forming at 10 instances as we speak’s fee. In the end, the galaxy churned out sufficient stars to populate half of its skinny disk. In different phrases, our galaxy would seem vastly completely different (and smaller) with out this current merger.
The speed of recent stars has been diminishing ever since. The analysis group’s simulation ends with the present-day Milky Manner making solely a solar-mass value of stars a 12 months, in settlement with different measurements.
The probability of such a current encounter finds help in cosmological simulations, which recommend Milky Manner-like galaxy has a excessive likelihood of swallowing up one other galaxy inside the final 10 billion years. For the extra observationally minded, there’s additionally a rising pile of research which have been discovering a sudden ramp-up in star formation 2–three billion years in the past.
If the Milky Manner actually did engulf its companion galaxy a pair billion years in the past, one factor’s for positive — our night time sky wouldn’t be the identical with out it.