How and when did the stars in the Universe form?
The Terzan 5 cluster contains many older, lower-mass stars (faint and in red), but also hotter, younger, higher-mass stars, some of which will generate iron and even heavier elements. It contains a mixture of Population I and Population II stars, indicating that this cluster has undergone several episodes of star formation. The different properties of the different generations can lead us to draw conclusions about the initial abundances of light elements and hold clues to the history of star formation in our cosmos.
To answer, we must look back through cosmic time.
Galaxies comparable to the current Milky Way have been numerous throughout cosmic time, having increased in mass and with a more evolved structure at the present time. Younger galaxies are inherently smaller, bluer, more chaotic, richer in gas, and have lower heavy element densities than their modern counterparts. Due to their large distances, it is impossible to resolve individual stars inside all but the nearest galaxies.
But individual stars can only be resolved in nearby galaxies.
This image, perhaps surprisingly, shows stars in the halo of the Andromeda galaxy. The bright star with diffraction peaks is from our Milky Way, while the individual bright spots observed are mostly stars from our neighboring galaxy: Andromeda. Beyond that, however, a wide variety of faint spots, galaxies in their own right, lie beyond. Individual stars can be resolved into galaxies up to tens of millions of light-years away, but that’s only one in a billion galaxies in total.
Large Milky Way-like galaxies form stars throughout their history.
The large spiral galaxy Messier 51, also known as the Whirlpool Galaxy, has extended and extended spiral arms, most likely due to its gravitational interactions with the neighboring galaxy shown to the right. Galaxies like this often have large waves of star formation occurring along their spiral arms, but only ~10% of the spirals exhibit the type of large spiral structure seen here.
But smaller galaxies formed stars all of a sudden, a long time ago, within our local group.
Most galaxies contain only a few star-forming regions: where the gas collapses, new stars form, and ionized hydrogen is found in a bubble surrounding this region. In a star galaxy, pretty much the entire galaxy itself is a star-forming region, with M82, the Cigar Galaxy just outside the Local Group, being the closest with these properties. Radiation from hot young stars ionizes a variety of atomic and molecular gases, particularly in the central region of the galaxy. Flares, supernovae and radiation will be common in these environments.
One of these galaxies is Wolf-Lundmark-Melotte: WLM, just 3.04 million light-years away.
This wide-field view shows the sky around the dwarf galaxy WLM in the constellation of Cetus (The Sea Monster). This image was created from images that are part of the Digitized Sky Survey 2. The bluish mass in the center of the image is the WLM galaxy; the bright, colorful, pointed dots, including the red and yellow dots, are simply prominent stars in our own Milky Way.
WLM, in the constellation of Cetus, is gravitationally bound to us, moving towards us at 122 km/s.
This map of many galaxies in the Local Group highlights the three largest members: Andromeda, the Milky Way, and the Triangle. The WLM galaxy, shown at the bottom of the image, lies about 3 million light-years from the Milky Way and is extremely isolated. It contains some of the oldest and most pristine stars in our cosmic backyard, close enough to be resolved by observatories such as JWST.
Much of its inner stars formed suddenly: 13 billion years ago.
This image, captured by ESO’s OmegaCAM on the VLT Survey Telescope, shows a lone galaxy known as Wolf-Lundmark-Melotte (WLM). Although considered part of our local cluster of dozens of galaxies, WLM stands alone on the periphery of the cluster as one of its outermost members. Its isolation from all other members of the local group is remarkable and helps provide a unique window into our cosmic past.
These stars are extremely pristine, with only 0.6% of the heavy elements found in the Sun.
Here, on the outskirts of the Wolf-Lundmark-Melotte (WLM) dwarf galaxy, stars of varying colors and luminosities can be seen as revealed by ESO’s OmegaCAM on the VLT Survey Telescope. The galaxy is so isolated that it may never have interacted or merged with any other galaxy since its formation more than 13 billion years ago, and the metal-poor stars it contains put prominently here, corroborate this image.
New stars are still forming sporadically inside, but these “old” stars represent an ancient, relict population.
The only known globular cluster in WLM is also old and metal-poor.
This impressive globular cluster does not belong to the Milky Way, but rather to the dwarf galaxy WLM located about 3.04 million light years away. It is extremely metal-poor, but for some reason it is the only known globular cluster that belongs to WLM.
But JWST’s new view offers amazing new insights.
This view represents the full field of JWST’s NIRCam view of the WLM dwarf galaxy, located on the outskirts of the Local Group. The dust within this galaxy is distributed asymmetrically, much like the stars. The left regions of this image are located closer to the galactic center, while the right side represents regions further away, and therefore more pristine.
It’s a big improvement over Spitzer’s previous infrared sight.
Part of the Wolf–Lundmark–Melotte (WLM) dwarf galaxy captured by the Spitzer Space Telescope’s infrared camera (left) and the James Webb Space Telescope’s near-infrared camera (right). The images demonstrate Webb’s remarkable ability to resolve faint stars outside the Milky Way. The incredible side-by-side improvement in resolution, light-gathering power, and filter count can be seen immediately, even by an untrained eye, with these images.
Even its faint and faint stars are easily resolved.
Located several million light-years from the Milky Way, Andromeda, and Triangle galaxies, the Wolf-Lundmark-Melotte (WLM) dwarf galaxy is extremely isolated within our Local Group. The stars that reveal themselves within largely formed at the same time and a long time ago, which means we are indeed looking at a relic of the early universe when we examine this galaxy in sufficient detail, which provides JWST’s NIRCam instrument.
JWST’s NIRCam reveals several thousand individual objects.
This star-dense region of the interior of the Wolf-Lundmark-Melotte (WLM) dwarf galaxy contains a few bright, higher-luminosity stars, but most of the stars here are very old and very metal-poor, so which allows astronomers who hone in on these populations to uncover many facts about how these stars formed and evolved when the Universe was only a few hundred million years old.
Low-density regions exhibit more pristine stellar populations.
Regions of low stellar density and dust in the WLM dwarf galaxy lie near the periphery and have undergone very little star formation since a great, one-shot explosion 13 billion years ago. Studying these ancient stars can help us understand how stars formed in the early Universe, when less than a billion years had passed since the hot Big Bang.
The dustiest areas suggest dynamic pressure blasting.
The dustiest parts of the Wolf-Lundmark-Melotte (WLM) dwarf galaxy show evidence of small amounts of quiescent and ongoing star formation, as well as evidence that this gas is being pushed out by dynamic pressure. Perhaps, even though mergers and interactions have been rare for WLM, there are clumps of gaseous intergalactic matter within the local group that he regularly encounters.
Occasionally, background galaxies appear.
Part of the Wolf-Lundmark-Melotte (WLM) dwarf galaxy captured by the James Webb Space Telescope’s near-infrared camera. This region features some of the stars located in WLM, about 3 million light-years away, as well as many background galaxies of varying sizes and distances. The Universe, even when we look into a nearby galaxy, cannot help but reveal itself when we look through the eyes of JWST.
Scientific knowledge will reveal how stars were formed long ago in the pristine environment of the early Universe.
Artist’s impression of the environment in the early universe after the formation, life and death of the first trillions of stars. Although there are sources of light in the early Universe, light is very rapidly absorbed by interstellar/intergalactic matter until reionization is complete. Although JWST may one day reveal evidence for these early stars, the only stars that can be individually resolved are located in galaxies very close to our own.
Mostly Mute Monday tells an astronomical story in pictures, visuals and no more than 200 words. Talk less; smile more.
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