Most astronomically observed galaxies are alive.
Although there are many instances of multiple galaxies in the same region of space, they usually occur between two galaxies or in very dense regions of space, such as the centers of galaxy clusters. It’s extremely rare to see 5 galaxies interacting less than 1 million light-years apart, captured here by Hubble in beautiful detail. Because all of these galaxies are still forming new stars, they are all classified as „alive” by astronomers.
Alive, for a galaxy, means „actively forming stars.”
The southern pinwheel galaxy, Messier 83, displays many features common to our Milky Way, including spiral arms and a central bar, as well as spurs and minor arms. Pink areas show changes in hydrogen atoms driven by UV light. Because that light is primarily produced by hot, blue stars, new star formation is actively occurring only where those pink features appear.
Many massive star-forming regions line the spiral arms of our Milky Way.
This ground-based, wide-field image of the Eagle Nebula shows the star-forming region in all its glory with new stars, reflection and emission nebulae, and dusty features. How matter around stars is ionized, and over time becomes transparent to all forms of light. Star-forming regions in the Milky Way are few in number and small in nature, especially compared to the more active galaxies in our universe.
As new stars form, they come with different masses and colors.
In the (modern) Morgan-Keenan spectral classification system, the temperature range for each star class is shown in Kelvin. The vast majority of stars today (80%) are M-class stars, with only about 1 in 800 being an O-class or B-class star, sufficient for a core-sols supernova. Our Sun is a G-class star, unremarkable but brighter than ~5% of stars. While mass generally determines a star’s color lifetime, many factors can influence a star’s evolution.
Although they all form at the same time, the hotter, bluer, shorter-lived stars evolve and die first.
The central concentration of this young star cluster at the heart of the Tarantula Nebula is called R136 and contains many of the most massive stars known. Among them is R136a1, which comes in at about ~260 solar masses, the largest known star. Brighter, bluer stars dominate this image, although there are a large number of cooler, redder stars.
A few galaxies – mostly ellipticals within the cluster – stopped forming stars long ago.
This large chain of galaxies is found near the center of the Perseus galaxy, many of which are found in the centers of massive, bright, evolved galaxies. For many of these galaxies, the stars found inside them are primarily old and red, with only a small population of blue stars found inside.
Over time, heavier, bluer stars die.
By mapping the colors and sizes of stars born at the same time, such as members of a cluster or globular cluster, we can identify where the main sequence ends and the heavier, more massive stars, and determine the age of the cluster. „Extinguished” and began to develop into subdivisions. A key to understanding the age of a stellar population is to fine tune the subpopulations.
Because red stars survive, galaxies without a new stellar population are called „red and dead” by astronomers.
Galaxy clusters, such as Abell S740, are the largest bound structures in the universe. When spirals merge, for example, large numbers of new stars are formed, but by rapid passage through the post-merger or intra-cluster medium, the gas is stripped away, leading to the end of star formation in that galaxy. A red and dead final texture.
Measuring the intrinsic color of a galaxy’s starlight determines whether a galaxy is dead or alive.
The massive galaxy cluster SDSS J1004+4112 is a massive collection of matter that has separated the universe from the galaxies within it and gravitationally lensed galaxies magnified by the gravitational pull of the foreground cluster. The different interstellar colors found within the central cluster highlight the enormous intracluster variability in the underlying stellar population.
Mainstream astronomy says that reserves of molecular gas within galaxies form new stars.
This image contains data from 10 different JWST filters: 6 in the near-infrared and 4 in the mid-infrared. As a result, features including stars, gas, dust and various molecular signatures can be revealed all at once, showing where star formation is occurring and likely to occur in the future. Molecular gas, which is abundant, is important.
If a galaxy has no new stars, it must be gasless.
The 'red and dead’ galaxy NGC 1277 is found within the Perseus cluster. While other galaxies have a mix of red and blue stars, this galaxy hasn’t formed new stars in about 10 billion years.
Gas can also be removed through periods of intense star formation, which are often fueled by mergers and interactions.
Galaxies undergoing massive bursts of star formation eject large amounts of material at high speeds. Thanks to hydrogen emissions, they glow red, covering the entire galaxy. This particular galaxy, M82, the Cigar Galaxy, is gravitationally interacting with its neighbor, M81, causing this explosive activity.
Rapid transits through the intergalactic medium of a galaxy cluster can also remove internal gas.
Located within the Norma cluster of galaxies, ESO 137-001 is accelerating through the intracluster medium, where interactions between matter in the space between the galaxies and the fast-moving galaxy produce ram pressure, leading to a new population of tidal streams. Intergalactic stars. Continued interactions like this eventually strip away all the gas in a galaxy.
In 2018, the first A red and dead galaxy in our cosmic backyard Identified: NGC 1277.
At 900 km/s it has not formed new stars in ~10 billion years through the Perseus cluster.
The galaxy NGC 1277 is speeding through the Perseus cluster, with not only red stars, but also red (and not blue) globular clusters, as well as an unusually large supermassive black hole speeding through this rich galaxy cluster.
Its stars and globular clusters are exclusively red.
A blink comparison plots the location of the dominant red and blue stars in the globular clusters in the galaxies NGC 1277 and NGC 1278. This is evidence that galaxy NGC 1277 stopped forming new stars several billion years ago, compared to NGC 1278, which has more young blue star clusters.
No new stars can form by then, unless gas reserves are replenished.
This map shows the distribution of globular clusters sorted by star color within the field of view of the Perseus cluster, which includes the neighboring galaxies NGC 1277 and NGC 1278. 1277 shows itself red and dead. Some studies suggest that no new stars formed by then for about 10 billion years.
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