Astronomers have produced the largest and most detailed map ever made of the vast web of cold cosmic gas stretching across the heart of our galaxy, showing thread-like filaments resembling rivers of material flowing through space that sometimes converge into bright clouds where new stars form.
Using the Chile-based ALMA telescope, the researchers examined the dynamics and chemistry of the Milky Way's central region, a chaotic and energetic expanse that serves as an enormous reservoir of raw material for making stars.
The region harbors dense clouds of gas and dust. The gas is mostly hydrogen, along with helium and others in trace amounts, all at frigid temperatures slightly above absolute zero. Stars form when clumps of gas and dust collapse under their own gravitational pull.
The supermassive black hole called Sagittarius A* resides at the galaxy's center. It sits within a region measuring about 650 light-years across that was observed using ALMA as part of a project exploring how gas condenses into stars in the extreme environment of the galactic core. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).
"For the first time, we can trace this gas continuously across the entire region at high resolution. That allows us to connect large-scale gas flows with the dense clouds where stars are forming, and to see how stellar explosions and radiation are reshaping the environment," said astronomer Ashley Barnes of the European Southern Observatory in Germany, one of the leaders of the research being published in six scientific papers in the journal Monthly Notices of the Royal Astronomical Society.
The region, called the Central Molecular Zone, is roughly 26,000 light-years from Earth. The area mapped, in the direction of the constellation Sagittarius, is about three times the width of the moon, as seen from Earth.
The researchers released an image showing ALMA's observations.
"Even though the image represents cold gas invisible to our eyes, when we assign colors to different (chemical) signals it reveals a striking and intricate landscape. There is a natural beauty in seeing the structure of our own galaxy laid out in such detail. What makes it especially powerful is knowing that these delicate-looking filaments are actually enormous structures, each spanning tens of light-years," Barnes said.
In addition to the filaments of gas, the image shows large cavities and bubble-like structures carved out by powerful winds and supernova explosions from massive stars populating the area.
There is an anomaly concerning star formation in this region.
"Despite containing enormous quantities of gas, it's forming far fewer stars than we'd expect. That's one of the big puzzles in astrophysics," said astrophysicist Steven Longmore of Liverpool John Moores University in England, another of the research leaders, and the current project is supplying data needed to solve it.
Unlike in the calmer spiral arms of the Milky Way, like the one the sun inhabits, the dynamics of its central region appear to interfere with star formation.
"The pressures are orders of magnitude higher. The magnetic fields are stronger," Longmore said.
"It's bathed in intense cosmic rays and radiation from the supermassive black hole and from the massive young stars that live there. And the turbulence is extraordinary. Gas is moving at highly supersonic speeds, clouds are colliding and the gravitational forces from the black hole and surrounding stars are constantly shearing and stretching the gas," Longmore said.
Sagittarius A* has a mass about 4 million times greater than the sun.
The researchers sketched out the complex chemistry of the region. For example, they spotted silicon monoxide, produced in violent shockwaves when gas clouds collide at supersonic speeds.
There also are complex organic molecules such as methanol, ethanol and acetone.
"These are particularly exciting because some of them are thought to be precursors to amino acids and other molecules essential for life," Longmore said. "Finding them in such abundance at the center of the galaxy tells us that even in these violent, extreme conditions, the chemistry of complexity - the chemistry that ultimately leads to biology - is thriving."
