New ESO Images Reveal Features of Nearby Galaxies


Using the most advanced telescopes on Earth and in orbit, like the European Southern Observatory’s Very Large Telescope (ESO’s VLT), scientists have gained unprecedented access to nearby galaxies, investigating how clouds of cold gas combine into hot balls of nuclear fusion giving birth to stars. The Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, is helping to figure out what causes gas to form stars.

Stars are born in clouds of gas but what triggers them and how galaxies take part is still a mystery to astronomers. However, these amazing images show different components of the galaxies in distinct colours enabling astronomers to identify the locations of young stars and the gas that warms around them. These stellar nurseries hold the secrets of how clouds of cold gas ignite to become stars.   

The work is part of the PHANGS (Physics at High Angular Resolution in Nearby GalaxieS) survey, which includes ESO’s Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA).

Emsellem, affiliated with the University of Lyon, France, released the latest set of galactic scans, taken with the Multi-Unit Spectroscopic Explorer (MUSE) instrument on ESO’s VLT in the Atacama Desert in Chile.

“For the first time, we are resolving individual units of star formation over a wide range of locations and environments in a sample that well represents the different types of galaxies,” says Eric Emsellem, an astronomer at ESO in Germany and lead of the VLT-based observations conducted as part of the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) project. “We can directly observe the gas that gives birth to stars, we see the young stars themselves, and we witness their evolution through various phases.”

ALMA combines radio wavelength signals from 66 dish-shaped antennas, the VLT consists of four large 8-metre telescopes and four smaller telescopes that can be used separately or combined into a single larger instrument.

This image, taken with the Multi-Unit Spectroscopic Explorer (MUSE), shows the nearby galaxy NGC 4254. NGC 4254 is an impressive spiral galaxy located roughly 45 million light-years from Earth in Coma Berenices’ constellation. The golden glows linked to clouds of ionised hydrogen, oxygen and sulphur gas, ushering the newly born stars. The bluish regions in the background show the cluster of relatively older stars.

“There are many mysteries we want to unravel,” says Kathryn Kreckel from the University of Heidelberg in Germany and PHANGS team member. “Are stars more often born in specific regions of their host galaxies — and, if so, why? And after stars are born, how does their evolution influence the formation of new generations of stars?”

Now the Astronomers will solve these questions with the help of data collected from MUSE and ALMA. MUSE collects bar codes to scan for the identification of cosmic objects. For this project, MUSE observed 30 000 nebulae of warm gas and collected about 15 million spectra of different galactic regions. In comparison, the ALMA enabled astronomers to map nearly 100 000 cold-gas regions across 90 nearby galaxies.

Subsequently, The PHANGS project also considers observations from the NASA/ESA Hubble Space Telescope. The various observations helped scan our galactic partners at various wavelengths.

“Their combination allows us to probe the various stages of stellar birth — from the formation of the stellar nurseries to the onset of star formation itself and the final destruction of the nurseries by the newly born stars — in more detail than is possible with individual observations,” says PHANGS team member Francesco Belfiore from INAF-Arcetri in Florence, Italy. “PHANGS is the first time we have been able to assemble such a complete view, taking images sharp enough to see the individual clouds, stars, and nebulae that signify forming stars.“

NASA’s James Webb Space Telescope will further improve the PHANGS project. This way, more data will be collected, enabling scientists to look into the structures of stellar nurseries more closely.

“As amazing as PHANGS is, the resolution of the maps that we produce is just sufficient to identify and separate individual star-forming clouds, but not good enough to see what’s happening inside them in detail,” pointed out Eva Schinnerer, a research group leader at the Max Planck Institute for Astronomy in Germany and principal investigator of the PHANGS project, under which the new observations were conducted. “New observational efforts by our team and others are pushing the boundary in this direction, so we have decades of exciting discoveries ahead of us.”

The international PHANGS project has a team of over 90 scientists around the globe. The MUSE data reduction working group is led by Eric Emsellem (European Southern Observatory, Garching, Germany and Centre de Recherche Astrophysique de Lyon, Université de Lyon, ENS de Lyon, Saint-Genis Laval, France) and includes Francesco Belfiore (INAF Osservatorio Astrofisico di Arcetri, Florence, Italy), Guillermo Blanc (Carnegie Observatories, Pasadena, US), Enrico Congiu (Universidad de Chile, Santiago, Chile and Las Campanas Observatory, Carnegie Institution for Science, Atacama Region, Chile), Brent Groves (The University of Western Australia, Perth, Australia), I-Ting Ho (Max Planck Institute for Astronomy, Heidelberg, Germany [MPIA]), Kathryn Kreckel (Heidelberg University, Heidelberg, Germany), Rebecca McElroy (Sydney Institute for Astronomy, Sydney, Australia), Ismael Pessa (MPIA), Patricia Sanchez-Blazquez (Complutense University of Madrid, Madrid, Spain), Francesco Santoro (MPIA), Fabian Scheuermann (Heidelberg University, Heidelberg, Germany) and Eva Schinnerer (MPIA).

ESO is the first intergovernmental astronomy organisation in Europe with 16 Member States, including Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a Strategic Partner. ESO works on the design, construction and operation of ground-based observing facilities. In addition, it operates three observing sites in Chile: La Silla, Paranal and Chajnantor.

At Paranal, ESO operates the world-leading Very Large Telescope Interferometer and two survey telescopes called VISTA and VLT.

ESO is partnered with APEX and ALMA, located in Chajnantor. And on Cerro Armazones, ESO is building the 39-metre Extremely Large Telescope, the ELT, which would be “the world’s biggest eye on the sky”.


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