Young, massive stars in the Triangulum Galaxy

Today’s Image of the Day from the European Space Agency features the star-forming region NGC 604, which is located 2.73 million light-years away from Earth in the Triangulum Galaxy (M33). The image was captured by the James Webb Space Telescope.

By studying regions like NGC 604, astronomers can gain insights into the complex interactions between stars and the interstellar medium, as well as the conditions that lead to the birth of stars. This, in turn, helps in understanding the evolution of galaxies and the universe as a whole.

Massive stars of NGC 604

“Sheltered among NGC 604’s dusty envelopes of gas are more than 200 of the hottest, most massive kinds of stars, all in the early stages of their lives,” said ESA.

“These types of stars are known as B-types and O-types, the latter of which can be more than 100 times the mass of our own Sun. It’s quite rare to find this concentration of them in the nearby universe. In fact, there’s no similar region within our own Milky Way galaxy.”

According to ESA, this concentration of massive stars, combined with its relatively close distance, means NGC 604 gives astronomers an opportunity to study these objects at a fascinating time early in their life.

Gigantic region of ionized hydrogen

NGC 604 is one of the largest known regions of ionized hydrogen, also known as an H II region. This nebula is significantly larger than the Orion Nebula, which is one of the most well-known H II regions in our own Milky Way galaxy. 

NGC 604 spans about 1,500 light-years across, making it one of the largest H II regions in the Local Group of galaxies. This group includes the Milky Way, the Andromeda Galaxy, and about 54 other smaller galaxies. 

NGC 604 starburst phenomenon

Within NGC 604, there are hundreds of young, hot, massive stars. These stars have ionized the surrounding gas, causing it to glow and creating the nebula. The region is a prime example of a starburst phenomenon, where stars form at a much higher rate than in typical galactic conditions.

“The bright orange streaks in this image signify the presence of carbon-based molecules known as polycyclic aromatic hydrocarbons, or PAHs,” explained ESA.

“As you travel further from the immediate cavities of dust where the star is forming, the deeper red signifies molecular hydrogen. This cooler gas is a prime environment for star formation. Ionized hydrogen from ultraviolet radiation appears as a white and blue ghostly glow.”

More about star formation

Star formation is crucial for the evolution of galaxies and the synthesis of heavy elements. In the cores of stars, elements heavier than helium are created.

The elements are spread throughout the galaxy when stars reach the end of their lives and expel their material – either gently through winds or violently via supernova explosions. This enriching process allows for the formation of new stars and planets, and ultimately, the potential for life.

Cloud collapse

The process begins when part of a molecular cloud becomes unstable and starts to collapse under its own gravity. This can be triggered by events like shock waves from nearby supernovae, galactic collisions, or the influence of other massive stars.

Formation of a protostar

As the cloud collapses, it fragments into smaller clumps. Each clump will eventually form one or more stars.

The material within these clumps continues to fall inward, heating up as it does so, eventually forming a warm core called a protostar. At this stage, the protostar is not yet hot enough for nuclear fusion (the process that powers stars) to occur.

Accretion disk

Around the protostar, material from the surrounding cloud continues to fall inward, forming a rotating disk. This material slowly accretes onto the protostar, increasing its mass.

Nuclear fusion begins

Once the core of the protostar reaches a high enough temperature and pressure, hydrogen atoms begin to fuse into helium, releasing energy in the process. This marks the transition from a protostar to a main sequence star, like our sun.

Main sequence and beyond

The star will spend the majority of its life in the main sequence stage, where it balances the gravitational forces trying to collapse it and the outward pressure from nuclear fusion.

Eventually, the star will exhaust its hydrogen fuel. Its subsequent evolution will depend on its initial mass, leading to various end stages such as red giants, supernovae, neutron stars, or black holes.

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

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