ALMA Discovers Proto Super Star Cluster — a Cosmic ‘Dinosaur Egg’ About to Hatch

Globular clusters – dazzling agglomerations of up to a million ancient stars – are among the oldest objects in the universe. Though plentiful in and around many galaxies, newborn examples are vanishingly rare and the conditions necessary to create new ones have never been detected, until now.

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered what may be the first known example of a globular cluster about to be born: an incredibly massive, extremely dense, yet star-free cloud of molecular gas.

“We may be witnessing one of the most ancient and extreme modes of star formation in the universe,” said Kelsey Johnson, an astronomer at the University of Virginia in Charlottesville and lead author on a paper accepted for publication in the Astrophysical Journal. “This remarkable object looks like it was plucked straight out of the very early universe. To discover something that has all the characteristics of a globular cluster, yet has not begun making stars, is like finding a dinosaur egg that’s about to hatch.”

This object, which the astronomers playfully refer to as the “Firecracker,” is located approximately 50 million light-years away from Earth nestled inside a famous pair of interacting galaxies (NGC 4038 and NGC 4039), which are collectively known as the Antennae galaxies. The tidal forces generated by their ongoing merger are triggering star formation on a colossal scale, much of it occurring inside dense clusters.

What makes the Firecracker unique, however, is its extraordinary mass, comparatively small size, and apparent lack of stars.

All other globular cluster analogues astronomers have observed to date are already brimming with stars. The heat and radiation from these stars have therefore altered the surrounding environment considerably, erasing any evidence of its colder, quieter beginnings.

With ALMA, the astronomers were able to find and study in detail a pristine example of such an object before stars forever change its unique characteristics. This afforded astronomers a first-ever glimpse of the conditions that may have led to the formation of many, if not all globular clusters.

“Until now, clouds with this potential have only been seen as teenagers, after star formation had begun,” said Johnson. “That meant that the nursery had already been disturbed. To understand how a globular cluster forms, you need to see its true beginnings.”

Most globular clusters formed during a veritable “baby boom” around 12 billion years ago, at a time when galaxies first assembled. Each contains as many as a million densely packed “second generation” stars — stars with conspicuously low concentrations of heavy metals, indicating they formed very early in the history of the universe. Our own Milky Way is known to have at least 150 such clusters, though it may have many more.

Throughout the universe, star clusters of various sizes are still forming to this day. It’s possible, though increasingly rare, that the largest and densest of these will go on to become globular clusters.

“The survival rate for a massive young star cluster to remain intact is very low – around one percent,” said Johnson. “Various external and internal forces pull these objects apart, either forming open clusters like the Pleiades or completely disintegrating to become part of a galaxy’s halo.”

The astronomers believe, however, that the object they observed with ALMA, which contains 50 million times the mass of the Sun in molecular gas, is sufficiently dense that it has a good chance of being one of the lucky ones.

Globular clusters evolve out of their embryonic, star-free stage very rapidly — in as little as one million years. This means the object discovered by ALMA is undergoing a very special phase of its life, offering astronomers a unique opportunity to study a major component of the early universe.

The ALMA data also indicate that the Firecracker cloud is under extreme pressure – approximately 10,000 times greater than typical interstellar pressures. This supports previous theories that high pressures are required to form globular clusters.

In exploring the Antennae, Johnson and her colleagues observed the faint emission from carbon monoxide molecules, which allowed them to image and characterize individual clouds of dust and gas. The lack of any appreciable thermal emission – the telltale signal given off by gas heated by nearby stars – confirms that this newly discovered object is still in its pristine, unaltered state.

Further studies with ALMA may reveal additional examples of proto super star clusters in the Antennae galaxies and other interacting galaxies, shedding light on the origins of these ancient objects and the role they play in galactic evolution.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

#  #  #

Contact: Charles Blue
NRAO Public Information Officer
Charlottesville, Virginia
Tel: (434) 296-0314
Email: [email protected]

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the US National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

“The Physical Conditions in a Pre Super Star Cluster Molecular Cloud in the Antennae Galaxies,” K. E. Johnson et al., 2015, to appear in the Astrophysical Journal [, preprint:].

In Other News…

ACEAP Ambassador Heads into Space as First African-American Woman to Pilot Spacecraft

Astronomy in Chile Educator Ambassadors Program participant pilots SpaceX Dragon spacecraftToday Sian Proctor, a participant in the Astronomy in Chile Educator Ambassadors Program (ACEAP) has successfully piloted the Inspiration4 mission carrying her and three other...

NSF Awards Funding for Next-Generation VLA Antenna Development

The National Science Foundation (NSF) has awarded the National Radio Astronomy Observatory (NRAO) $23 million for design and development work on the Next Generation Very Large Array (ngVLA), including producing a prototype antenna.

Andean Science Diplomacy: Interview with Chile’s Ambassador to the U.S., Ambassador Silva

Ambassador Alfonso Silva Navarro leads Chile’s Embassy to the United States since September 2018. His extensive diplomatic career includes being the Chilean Ambassador to Canada, India, and Jamaica, as well as being the Director General on Foreign Affairs at Chile’s Ministry of Foreign Affairs.

NANOGrav & Green Bank Telescope Poised to Make Groundbreaking Discoveries of Gravitational Wave Universe

For the next three years, astronomers from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) will have increased access and new technologies to use on the National Science Foundation’s Green Bank Telescope (GBT) in their breakthrough scientific studies of gravitational waves.

Astronomers make first clear detection of a moon-forming disc around an exoplanet

Using the Atacama Large Millimeter /submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, astronomers have unambiguously detected the presence of a disc around a planet outside our Solar System for the first time.

AUI and Accumen Partner to Increase Crisis Resilience to Natural and Manmade Disasters for Healthcare Sector

AUI and Accumen, Inc. announced they are partnering to provide services to improve crisis resilience to manmade and natural disasters for the healthcare sector at a historically challenging time.

New Scholarship Established by the AUI Board of Trustees

AUI and the National Radio Astronomy Observatory (NRAO) today announced the establishment of the AUI Board of Trustees NAC Bridge Scholarship Award.

2021 Jansky Lectureship Awarded to Mexican Astronomer

Associated Universities, Inc. (AUI) and the National Radio Astronomy Observatory (NRAO) have awarded the 2021 Karl G. Jansky Lectureship to Professor Luis F. Rodriguez of the National University of Mexico (UNAM).

Pride Month Statement

Pride Month is a time for celebration of LGBTQIA+ communities in commemoration of the Stonewall Uprising of 1969. At AUI, we celebrate an environment that is safe and welcoming to all, and the strength that our diversity brings us.

Cyber Expert Wins FBI Community Leadership Award

Robert R. Wells, special agent in charge of the Charlotte Division of the FBI has chosen a local cyber expert as the 2020 Director’s Community Leadership Award (DCLA) recipient for North Carolina. Torry Crass has been an invaluable partner to the FBI Charlotte field office since 2013.

You are now leaving AUI

You will be redirected to the related partnering organization's website.

You will be redirected to
in 4 seconds...

Click the link above to continue or CANCEL