Astrophysicists Uncover the Secrets Behind the Formation of Massive Galaxies

It’s both humbling and inspiring to consider how much remains to be discovered about the Universe. My collaborators and I recently addressed one of astrophysics’ longstanding mysteries: how massive elliptical galaxies form.

For the first time, we now have strong observational evidence to answer this question, as detailed in our recently published study in Nature.

Two Types of Galaxies

In today’s Universe, galaxies fall into two main categories. Spiral galaxies, like our Milky Way, are rich in gas and actively form stars in a rotating disc. On the other hand, elliptical galaxies are large, spherical structures resembling rugby balls. These galaxies no longer produce new stars, primarily hosting stars formed more than 10 billion years ago.

Explaining how elliptical galaxies evolved from flat, rotating discs to their current three-dimensional shape has posed a challenge for cosmological models. During the era when these galaxies formed, about 10 to 12 billion years ago, star formation was thought to occur within large rotating discs. This raises a critical question: how did these flat galaxies transform into the spherical ellipticals we see today?

Insights from ALMA Observations

Using data from the Atacama Large Millimeter/submillimeter Array (ALMA), we pinpointed the birthplaces of giant elliptical galaxies. Contrary to expectations, we discovered that elliptical galaxies formed through intense, short-lived episodes of star formation early in the Universe’s history, rather than starting as rotating discs that later evolved into elliptical shapes.

Our research analyzed the dust distribution in over 100 distant galaxies, active when the Universe was between 2.2 and 5.9 billion years old. Dust acts as a marker for gas—the raw material for star formation—allowing us to study star-forming regions in these galaxies.

Using an innovative observational technique, we found that dust in these galaxies was incredibly compact, unlike the structure of flat, disc-shaped galaxies. The three-dimensional geometry of these dust regions indicated that early star-forming galaxies were already spherical, closely resembling today’s elliptical galaxies.

To understand the underlying physical processes, we used cosmological computer simulations. These revealed that cold gas streams from surrounding galaxies, combined with interactions and mergers, drove gas and dust into dense cores at the centers of these early galaxies. This mechanism fueled rapid star formation and led to the compact, spherical shapes observed.

This process, common in the early Universe, explains the rapid formation of elliptical galaxies and adds a crucial piece to the puzzle of galaxy evolution.

A Breakthrough in Observational Techniques

Our findings were made possible by a novel method for analyzing ALMA data. Unlike traditional optical telescopes, ALMA uses interferometry—combining signals from multiple antennas to produce sharp images of distant galaxies. This advanced technique allowed us to measure dust distribution with unprecedented precision, significantly improving upon previous methods.

We relied on archival, open-access ALMA data collected over several years. This underscores the power of open data and international collaboration in driving scientific progress.

What’s Next?

Future observations with the James Webb Space Telescope (JWST) and the Euclid space telescope will map the distribution of stars in the distant ancestors of elliptical galaxies. The Extremely Large Telescope, with its 39-meter mirror, will offer unparalleled detail of star-forming cores in these galaxies.

Additionally, sharper observations of gas dynamics with ALMA and the Very Large Telescope will shed light on how gas flows into galaxy centers, fueling star formation and shaping the galaxies we see today. These advancements will deepen our understanding of the origins and evolution of the Universe’s largest galaxies.

Read Original Article: Science Alert

Read More: Scitke