How Galaxies Make Sure They Always Have Enough Gas to Form New Stars
Key Takeaway
Galaxies keep a balance between making stars and having enough gas. They do this with complex processes. These include supermassive black holes and their jets. Supermassive black holes are very large black holes found at the center of galaxies. Jets are streams of high-energy particles that shoot out from these black holes. These mechanisms help galaxies not use up all their star-forming gas too fast. This way, galaxies can keep making stars for billions of years.
Summary
- Star Formation: Spiral and barred spiral galaxies have regions rich in hydrogen gas where stars form.
- Early Galaxies: The first galaxies were small, composed of hydrogen and helium, with massive, short-lived stars.
- Regulation Mechanism: Supermassive black holes at the centers of galaxies regulate star formation through processes akin to breathing.
- Heart and Lungs Analogy: Black holes pulse like a heart, and jets of radiation and gas act like airways, slowing gas accretion and star formation.
- Simulation Studies: Computer simulations have shown black holes pulsing and creating ripples that support the galaxy’s gas environment.
- Observational Evidence: Ripples similar to those in simulations have been observed in galaxy clusters, supporting the theory.
- Implications: Understanding these mechanisms helps explain why galaxies aren’t as large as expected and remain vibrant for billions of years.
How Galaxies Make Sure They Always Have Enough Gas to Form New Stars
Look at most spiral or barred spiral galaxies and you will see multiple regions where stars are forming. These star-forming regions are comprised of mostly hydrogen gas with a few other elements for good measure. The first galaxies in the Universe had huge supplies of this star-forming gas. Left unchecked, they could have burned through the gas quickly, generating enormous amounts of star formation. Life fast, though, and die young for such an energetic burst of star formation would soon fizzle out, leaving behind dead and dying stars. In some way, it seems, galaxies regulate their star formation thanks to supermassive black holes at their center.
The Birth of the First Galaxies
The first galaxies formed about 400 to 700 million years after the Big Bang, during the Epoch known as Reionization. These early galaxies were small and faint, mostly composed of hydrogen and helium, and contained dense clusters of massive, short-lived Population III stars, the first generation of stars. The intense radiation from these stars ionized the surrounding gas, clearing the fog that permeated space and making the universe transparent for the first time. These primordial galaxies began merging and interacting, laying the foundation for the galaxy types seen today.
A New Study on Galaxy Regulation
A new study published in the Monthly Notices of the Royal Astronomical Society explores why galaxies are not as large as astronomers would expect. The research suggests that galaxies, even those that formed first, avoid an early death because they have mechanisms similar to “heart and lungs,” which regulate their “breathing.” Without these regulatory processes, our bodies and galaxies would have aged much faster, resulting in massive galaxies filled with dead and dying stars and devoid of new star formation.
Observations and Findings
Observations show that galaxies are not so big and full of dying stars having outgrown themselves. It seems something limits their ability to allow gas to form into stars. Astrophysicists at the University of Kent believe they may have the answer: galaxies could be controlling their growth rate through a process not too dissimilar to “breathing.” They compare the supermassive black hole at the center of a galaxy to a heart and the supersonic jets emerging from the poles with the radiation and gas they emit to airways feeding a pair of lungs.
The Heart and Lungs of Galaxies
The supermassive black holes pulse like a heart. These pulses create a shock front that moves back and forth along the jets. It’s like a diaphragm inflating and deflating the lungs. This process sends energy along the jet. It slowly counters the pull of gravity. It also slows down gas falling into the black hole and star formation. PhD student Carl Richards developed this idea. His simulations showed a black hole pulsing like a heart.
In an illustration, magnetic fields help a spiraling wind to grow the supermassive black hole in galaxy ESO320-G030. A rotating wind of dense gas flows outward from the hidden supermassive black hole at the galaxy’s center. This wind dominates the galaxy’s core. Scientists traced the gas motions using light from hydrogen cyanide molecules. They measured these movements with the Atacama Large Millimeter/submillimeter Array, which is a powerful telescope.
Richards explains,
“We realized that there would have to be some means for the jets to support the body – the galaxy’s surrounding ambient gas – and that is what we discovered in our computer simulations.” He continued, “The unexpected behavior was revealed when we analyzed the computer simulations of high pressure and allowed the heart to pulse.”
Supporting Evidence from Observations
Evidence of ripples just like those in Richards’ simulations in extra-galactic media has been found in galaxy clusters like the Perseus cluster. These ripples are thought to sustain a galaxy’s environment, though their generation mechanism was unclear. Conventional simulations fail to explain gas flows into galaxies, but the work of the team from the University of Kent may well have answered the question.
The Role of Supermassive Black Holes
Supermassive black holes play a crucial role in regulating the gas supply in galaxies. They are not just passive objects but active participants in the galactic ecosystem. By emitting jets of radiation and particles, they can heat up the surrounding gas, preventing it from cooling down and collapsing to form stars. This process, known as feedback, ensures that the galaxy does not deplete its gas supply too quickly.
Mechanisms of Gas Regulation
- Feedback from Supermassive Black Holes: As mentioned, the jets from these black holes heat the gas and prevent it from collapsing to form stars. This feedback can be continuous or occur in bursts, depending on the activity of the black hole.
- Galactic Winds: Star formation itself can drive winds that push gas out of the galaxy. These winds are powered by the radiation and stellar winds from massive stars and by supernova explosions. The expelled gas can later cool and fall back into the galaxy, replenishing the gas supply.
- Gas Accretion from the Intergalactic Medium: Galaxies can also accrete gas from the intergalactic medium, the vast space between galaxies. This process can provide a fresh supply of gas for star formation.
Table 1: Mechanisms Regulating Gas Supply in Galaxies
| Mechanism | Description |
|---|---|
| Feedback from Black Holes | Jets from black holes heat surrounding gas, preventing star formation |
| Galactic Winds | Winds driven by star formation push gas out of the galaxy |
| Gas Accretion | Galaxies accrete gas from the intergalactic medium |
The Balance of Star Formation and Gas Supply
The balance between star formation and gas supply is delicate. If a galaxy forms stars too quickly, it will exhaust its gas supply and star formation will cease. If it forms stars too slowly, it will not be able to maintain its structure and will lose gas to the intergalactic medium. The regulatory mechanisms described above help galaxies maintain this balance.
Future Research Directions
Understanding how galaxies regulate their gas supply and star formation is an ongoing area of research. Future studies will focus on:
- Detailed Observations: Using advanced telescopes and instruments to observe the gas flows and feedback processes in galaxies.
- Improved Simulations: Developing more accurate simulations to model the complex interactions between stars, gas, and black holes.
- Comparative Studies: Comparing different types of galaxies to understand how these mechanisms vary across the galaxy population.
Table 2: Future Research Directions in Galaxy Regulation
| Research Area | Goals |
|---|---|
| Detailed Observations | Observe gas flows and feedback processes |
| Improved Simulations | Model interactions between stars, gas, and black holes |
| Comparative Studies | Understand variation of mechanisms across different galaxy types |
Conclusion
Galaxies have evolved complex mechanisms to ensure they always have enough gas to form new stars. The interplay between supermassive black holes, feedback processes, and gas accretion helps regulate the gas supply, preventing galaxies from exhausting their star-forming material too quickly. By studying these processes, astronomers can gain a deeper understanding of galaxy evolution and the life cycle of galaxies.
