Dwarf galaxy provides a window into the early universe

Today’s Image of the Day from the European Space Agency features the galaxy I Zwicky 18, which was captured in remarkable detail by the James Webb Space Telescope.

I Zwicky 18 is a blue compact dwarf galaxy located approximately 59 million light-years away in the constellation Ursa Major. 

Star formation in I Zwicky 18

The galaxy is notable for its relatively young appearance and the fact that it contains very few heavy elements. These characteristics indicate that it has experienced little star formation compared to other galaxies of similar age.

“The galaxy was first identified by Swiss astronomer Fritz Zwicky in the 1930’s and resides roughly 59 million light-years from Earth,” noted ESA. “This galaxy has gone through several sudden bursts of star formation.” 

According to ESA, I Zwicky 18 is typical of the kinds of galaxies that inhabited the early universe and is much smaller than our Milky Way.

Webb telescope image of the galaxy

“Two major starburst regions are embedded in the heart of the galaxy. The wispy brown filaments surrounding the central starburst region are bubbles of gas that have been heated by stellar winds and intense ultraviolet radiation unleashed by hot, young stars,” noted ESA.

“A companion galaxy resides nearby to the dwarf galaxy, which can be seen at the bottom of the wider-field image. The companion may be interacting with the dwarf galaxy and may have triggered that galaxy’s recent star formation.” 

ESA explained that the “orange blobs” surrounding the galaxy are the dim glow from ancient fully formed galaxies at much larger distances.

Key characteristics of I Zwicky 18

As previously mentioned, the galaxy has a very low abundance of elements heavier than hydrogen and helium, suggesting that it has not undergone significant stellar processing.

Young stellar population 

Despite its old age, I Zwicky 18 contains many young, hot stars. This suggests that it might have experienced a burst of star formation relatively recently in its history.

Interstellar medium 

The galaxy has a high density of gas, which is a prime ingredient for star formation. This gas is mostly in the form of hydrogen.

Unusual characteristics

Its characteristics are more typical of primordial galaxies found in the early universe, making it a valuable object of study for understanding galaxy formation and evolution.

Ultimately, I Zwicky 18 provides insights into the conditions and processes that might have been prevalent in the early universe.

Life cycles of stars and dust

The image was captured as part of a Webb program to study the life cycle of dust in I Zw 18. 

“Scientists are now building off of previous research with Hubble obtained at optical wavelengths, studying individual dusty stars in detail with Webb’s equivalent spatial resolution and sensitivity at infrared wavelengths.” 

ESA noted that this galaxy is of particular interest as its content of elements heavier than helium is one of the lowest of all known galaxies in the local universe. 

“Such conditions are thought to be similar to those in some of the first star-forming galaxies at high redshift, so the Webb study of I Zw 18 should shed light on the life-cycle of stars and dust in the early universe.”

The constellation Ursa Major

Ursa Major, also known as the Great Bear, is one of the most prominent and easily recognizable constellations in the northern sky.

Its name, “Ursa Major,” means “Great Bear” in Latin, and it has been a significant part of various mythologies and star lore across cultures for thousands of years.

One of the most famous asterisms within Ursa Major is the Big Dipper, a group of seven bright stars that form a shape resembling a ladle or dipper. The Big Dipper is often used as a navigation tool because it points to Polaris, the North Star, located in the nearby constellation Ursa Minor.

Ursa Major is best viewed in the northern hemisphere and is circumpolar, meaning it is visible year-round for much of the Northern Hemisphere. Its position changes with the seasons, rotating around Polaris, the North Star.

Image Credit: NASA/ESA/CSA James Webb Space Telescope

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