A spiral hiding an impostor

UGC 5460

A spiral galaxy seen close to face-on. The centre of its disc is a bright, pale yellowish oval shape. Spiral arms extend from either side of the oval through the disc on irregular paths. They are marked throughout by bright bluish-white patches of stars. Distant background galaxies appear as small orangish blobs around the spiral galaxy. In the top-left corner a nearby star shines brightly, spikes radiating from it. Credit: ESA/Hubble & NASA, W. Jacobson-Galán, A. Filippenko, J. Mauerhan

The sparkling spiral galaxy gracing this NASA/ESA Hubble Space Telescope Picture of the Week is UGC 5460, which sits about 60 million light-years away in the constellation Ursa Major. This image combines four different wavelengths of light to reveal UGC 5460’s central bar of stars, winding spiral arms and bright blue star clusters. Also captured in the upper left-hand corner of this image is a far closer object: a star just 577 light-years away in our own galaxy.

UGC 5460 has hosted two recent supernovae named SN 2011ht and SN 2015as. It’s because of these two stellar explosions that Hubble targeted this galaxy, collecting data for three observing programmes that aim to study various kinds of supernovae.

SN 2015as was what’s known as a core-collapse supernova: a cataclysmic explosion that happens when the core of a star far more massive than the Sun runs out of fuel and collapses under its own gravity, initiating a rebound of material outside the core. Hubble observations of SN 2015as will help researchers understand what happens when the expanding shockwave of a supernova collides with the gas that surrounds the exploded star.
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SN 2011ht might have been a core-collapse supernova as well, but it could also be an impostor called a luminous blue variable. Luminous blue variables are rare stars that experience eruptions so large that they can mimic supernovae. Crucially, luminous blue variables emerge from these eruptions unscathed, while stars that go supernova do not. Hubble will search for a stellar survivor at SN 2011ht’s location, and the explosion’s identity may be revealed at last.

Source: ESA/Hubble/potw

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NASA's Webb Probes an Extreme Starburst Galaxy

M82 (Hubble and Webb)
Credit: Image: NASA, ESA, CSA, STScI, Alberto Bolatto (UMD)

M82 (NIRCam Image)
Credit: Image: NASA, ESA, CSA, STScI, Alberto Bolatto (UMD)

M82 (NIRCam Image)
Credit: Image: NASA, ESA, CSA, STScI, Alberto Bolatto (UMD)

Images

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A team of astronomers has used NASA’s James Webb Space Telescope to survey the starburst galaxy Messier 82 (M82). Located 12 million light-years away in the constellation Ursa Major, this galaxy is relatively compact in size but hosts a frenzy of star formation activity. For comparison, M82 is sprouting new stars 10 times faster than the Milky Way galaxy.

Led by Alberto Bolatto at the University of Maryland, College Park, the team directed Webb’s NIRCam (Near-Infrared Camera) instrument toward the starburst galaxy’s center, attaining a closer look at the physical conditions that foster the formation of new stars.

“M82 has garnered a variety of observations over the years because it can be considered as the prototypical starburst galaxy,” said Bolatto, lead author of the study. “Both NASA’s Spitzer and Hubble space telescopes have observed this target. With Webb’s size and resolution, we can look at this star-forming galaxy and see all of this beautiful, new detail.”

A Vibrant Community of Stars

Star formation continues to maintain a sense of mystery because it is shrouded by curtains of dust and gas, creating an obstacle in observing this process. Fortunately, Webb’s ability to peer in the infrared is an asset in navigating these murky conditions. Additionally, these NIRCam images of the very center of the starburst were obtained using an instrument mode that prevented the very bright source from overwhelming the detector.

While dark brown tendrils of heavy dust are threaded throughout M82’s glowing white core even in this infrared view, Webb’s NIRCam has revealed a level of detail that has historically been obscured. Looking closer toward the center, small specks depicted in green denote concentrated areas of iron, most of which are supernova remnants. Small patches that appear red signify regions where molecular hydrogen is being lit up by a nearby young star’s radiation.

“This image shows the power of Webb,” said Rebecca Levy, second author of the study at the University of Arizona in Tucson. “Every single white dot in this image is either a star or a star cluster. We can start to distinguish all of these tiny point sources, which enables us to acquire an accurate count of all the star clusters in this galaxy.”

Finding Structure in Lively Conditions

Looking at M82 in slightly longer infrared wavelengths, clumpy tendrils represented in red can be seen extending above and below the galaxy’s plane. These gaseous streamers are a galactic wind rushing out from the core of the starburst.

One area of focus for this research team was understanding how this galactic wind, which is caused by the rapid rate of star formation and subsequent supernovae, is being launched and influencing its surrounding environment. By resolving a central section of M82, scientists could examine where the wind originates, and gain insight on how hot and cold components interact within the wind.

Webb’s NIRCam instrument was well-suited to trace the structure of the galactic wind via emission from sooty chemical molecules known as polycyclic aromatic hydrocarbons (PAHs). PAHs can be considered as very small dust grains that survive in cooler temperatures but are destroyed in hot conditions.

Much to the team’s surprise, Webb’s view of the PAH emission highlights the galactic wind’s fine structure – an aspect previously unknown. Depicted as red filaments, the emission extends away from the central region where the heart of star formation is located. Another unanticipated find was the similar structure between the PAH emission and that of hot, ionized gas.

“It was unexpected to see the PAH emission resemble ionized gas,” said Bolatto. “PAHs are not supposed to live very long when exposed to such a strong radiation field, so perhaps they are being replenished all the time. It challenges our theories and shows us that further investigation is required.”

Lighting a Path Forward

Webb’s observations of M82 in near-infrared light spur further questions about star formation, some of which the team hopes to answer with additional data gathered with Webb, including that of another starburst galaxy. Two other papers from this team characterizing the stellar clusters and correlations among wind components of M82 are almost finalized.

In the near future, the team will have spectroscopic observations of M82 from Webb ready for their analysis, as well as complementary large-scale images of the galaxy and wind. Spectral data will help astronomers determine accurate ages for the star clusters and provide a sense of timing for how long each phase of star formation lasts in a starburst galaxy environment. On a broader scale, inspecting the activity in galaxies like M82 can deepen astronomers’ understanding of the early universe.

“Webb’s observation of M82, a target closer to us, is a reminder that the telescope excels at studying galaxies at all distances,” said Bolatto. “In addition to looking at young, high-redshift galaxies, we can look at targets closer to home to gather insight into the processes that are happening here – events that also occurred in the early universe.”

These findings have been accepted for publication in The Astrophysical Journal.

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Source: NASA's James Webb Space Telescope/News

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About This Release

Credits:

Media Contact:

Abigail Major
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Alberto Bolatto (UMD)

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team

Related Links and Documents

• The science paper by A. Bolatto et al.
• The Max Planck Institute for Astronomy Press Release

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Faintest Known Star System Orbiting the Milky Way Discovered from Hawaiʻi

An image of uma3/u1, a tiny cluster of ancient stars captured by CFTH
Credit: CFHT/S. Gwyn

Maunakea, Hawaiʻi - A team of astronomers led by the University of Victoria and Yale University has detected an ancient star system traveling around our galaxy named Ursa Major III / UNIONS 1 (UMa3/U1) – the faintest and lowest-mass Milky Way satellite ever discovered, and possibly one of the most dark matter-dominated systems known.

The team conducted the study from Hawaiʻi using two Maunakea Observatories on Hawaiʻi Island – W. M. Keck Observatory and Canada-France-Hawaiʻi Telescope (CFHT) – as well as the University of Hawaiʻi Institute for Astronomy Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) on Haleakalā, Maui; the findings are published in a recent edition of The Astrophysical Journal.

“UMa3/U1 is located in the Ursa Major (Great Bear) constellation, home of the Big Dipper. It is in our cosmic backyard, relatively speaking, at about 30,000 light-years from the Sun,” says Simon Smith, an astronomy graduate student at University of Victoria and lead author of the study. “UMa3/U1 had escaped detection until now due to its extremely low luminosity.”

Observations reveal the stellar system is tiny, with only about 60 stars that are over 10 billion years old spanning just 10 light years across. UMa3/U1 has an extremely low mass – at 16 times the mass of the Sun, it is 15 times less massive than the faintest suspected dwarf galaxy.

UMa3/U1 was first detected using data obtained from the Ultraviolet Near Infrared Optical Northern Survey (UNIONS) at CFHT and Pan-STARRS.

The team then studied the star system in finer detail using Keck Observatory’s Deep Imaging Multi-Object Spectrograph (DEIMOS) and confirmed UMa3/U1 is a gravitationally-bound system, either a dwarf galaxy or a star cluster.

“There are so few stars in UMa3/U1 that one might reasonably question whether it’s just a chance grouping of similar stars. Keck was critical in showing this is not the case,” says co-author Marla Geha, professor of astronomy and physics at Yale University. “Our DEIMOS measurements clearly show all the stars are moving through space at very similar velocities and appear to share similar chemistries.”

Hidden in this deep sky image (left) is Uma3/U1, a miniscule group of stars (right) bound together by their own gravity (and possibly even dark matter!) in orbit around the Milky Way. Credit: CFHT/S. Gwyn (right) / S. Smith (left)

“Excitingly, a tentative spread in velocities among the stars in the system may support the conclusion that UMa3/U1 is a dark matter-dominated galaxy – a tantalizing possibility we hope to scrutinize with more Keck observations,” says Yale University graduate student Will Cerny, the second author of the study.

How these stars have managed to stay a tight-knit group is remarkable. One possible explanation is that dark matter may be keeping them together.

“The object is so puny that its long-term survival is very surprising. One might have expected the harsh tidal forces from the Milky Way’s disk to have ripped the system apart by now, leaving no observable remnant,” says Cerny. “The fact that the system appears intact leads to two equally interesting possibilities. Either UMa3/U1 is a tiny galaxy stabilized by large amounts of dark matter, or it’s a star cluster we’ve observed at a very special time before its imminent demise.”

With the former scenario, achieving direct confirmation of UMa3/U1 as a faint, ancient, dark matter-dominated satellite star system would be an exciting feat because it would support a prediction in the leading theory for the universe’s origin. Under the Lambda Cold Dark Matter (LCDM) model, scientists hypothesize that when galaxies like the Milky Way first formed, they created a gravitational pull during their assembly process that attracted hundreds of satellite star systems which continue to orbit galaxies today.

A companion study on UMa3/U1’s implications on the LCDM theory has been accepted for publication in The Astrophysical Journal and is available in preprint format on arXiv.org.

“Whether future observations confirm or reject that this system contains a large amount of dark matter, we’re very excited by the possibility that this object could be the tip of the iceberg – that it could be the first example of a new class of extremely faint stellar systems that have eluded detection until now,” says Cerny.

Conclusive evidence of the presence or lack of dark matter in UMa3/U1 is key to determining whether the star system is a dwarf galaxy or a star cluster. Until its classification becomes clear, Ursa Major III / UNIONS 1 has two names. Ultra-faint Milky Way satellites are typically named after the constellation they are discovered in (in this case, Ursa Major) whereas ultra-faint star clusters are generally named after the survey project they were discovered in (UNIONS).

While this star system’s identity is still ambiguous, UMa3/U1 paves the way for new perspectives in cosmology.

“This discovery may challenge our understanding of galaxy formation and perhaps even the definition of a ‘galaxy’,” says Smith.

Source: W. M. Keck Observatory/News

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About DEIMOS

The DEep Imaging and Multi-Object Spectrograph (DEIMOS) boasts the largest field of view (16.7arcmin by 5 arcmin) of any of the Keck Observatory instruments, and the largest number of pixels (64 Mpix). It is used primarily in its multi-object mode, obtaining simultaneous spectra of up to 130 galaxies or stars. Astronomers study fields of distant galaxies with DEIMOS, efficiently probing the most distant corners of the universe with high sensitivity.

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About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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