When it came to stealing stars, Milky Way's closest galactic neighbors went to a slow start. But they are gaining momentum now.
By making the first detailed chemical maps of a galaxy beyond our own, the researchers found that star formation in the large and small magellanic clouds has spiked lately, after a delay. The new results not only provide insight into the richest type of galaxies in the universe, but also help improve understanding of Growth development.
Although the large and small magellanic clouds (LMC and SMC respectively) lie only 150,000 light-years from the Milky Way – right next to, astronomically speaking, astronomers have found it difficult to study their composition. [Dizzying Array of Stars Dazzles in New Hubble Photo]
"It has been challenging to map their full structure," said David Nidever, an astronomer at Montana State University, last month at the 23rd American Astronomical Society meeting in Seattle. Nidever and his colleagues used the study of the experimental patient Galaxy Evolution Experiment 2 (APOGEE-2) to obtain accurate observations of 5,000 stars in Magellanic Clouds. By mapping out how heavy elements are distributed through the stars in the galaxy, astronomers could model roughly when generations of stars were born.
"With this new ability we can study Magellanic Clouds like never before," Nidever said.
A slow start
Only visible from the southern hemisphere, LMC and SMC were named after the explorer Ferdinand Magellan, who led the first European expedition to circulate the globe. The couple are dwarf salmon, smaller collections of stars that can hold anywhere from 1
Although qualified as dwarf galaxies, LMC and SMC are unusual, building stars much slower than their counterparts. The difference has been a long mystery for researchers.
"There must be a relationship between the mass of the galaxy and early star formation speeds," Nidever told Space.com. "The Magellanic Clouds are falling far away from the trend."
Sloan Digital Sky Survey's APOGEE-1 project studied the Northern Hemisphere's Milky Way from 2011 to 2014, providing "unprecedented insight into the dynamic structure and chemical history of galaxies," according to Sloan's website. Based in New Mexico, the first version of APOGEE was limited to the northern hemisphere.
In 2017, the almost identical instrument APOGEE-2 was installed at Las Campanas Observatory in Chile. The instrument began to observe LMC and SMC that year.
The first stars formed from dense clouds of hydrogen and helium and converted a small percentage of the gas into heavier elements. As they exploded in violent supernovae, they sowed their surroundings with these elements, which were drawn into the next generation of stars, and the bike continued – with each generation of stars converting more stock into heavier elements.
With APOGEE-2, Nidever and his colleagues were able to probe the chemical make-up of thousands of stars in the LMC and SMC. The researchers folded this makeup into simulations to determine how long it took generations of stars to form. In this way, they could reconstruct the star storage history of both galaxies.
Unlike the Milky Way, Magellanic Clouds came to a slow start and built new stars about 50 times slower than our own galaxy, Nidever said. But despite this lazy start, the LMC had a new kick that led to a six-fold in new stars.
"It's never too late to become active," Nidever said.
What caused the latest blow-up that happened about 2 billion years ago? Nidever said the most likely source is that a recent brush with SMC burned starburst in the larger dwarf galaxy.
"We can see features that they have interacted with in their structure," Nidever said.
The Clouds Slow Starts Opposite to Other Dwarf Laxes Around the Milky Way. Star formation speeds in the pair are even lower than expected for their mass, Nidever said.
"It's a kind of mystery," he said.
The difference is probably due to different environments. Most of the dwarf galaxies studied so far have made several trips around the Milky Way. Their gravity interactions with our galaxy may have helped turn their gas into stars.
However, LMC and SMC most likely take their very first spin around the growth path, according to previous studies. That means they spent about 10 billion years building stars isolated, without a massive galaxy to increase their starbirth, the researchers said. Only in the last few billion years have the couple started to interact more often with the Milky Way and with each other, increasing how quickly they build their stars.
But things are just getting started for LMC and SMC. For about 2.5 billion years, the LMC will merge with the Milky Way and set aside a flurry of star formation.
"Many of the stars [in the Magellanic Clouds] will be thrown into Vetstens halo and will dramatically affect the makeup of his halo," Nidever said.
The merger will cause an outbreak of star formation in the remaining gas and dust of the Magellanic Clouds, he added. After settling for such a slow start, the couple will pack their last year in a storm of star-like fireworks.
The research is submitted to the Astrophysical Journal and is available on the preprint server arXiv.