Question How do stars form?

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Apr 13, 2021
Rather than giving you my opinion, , please make your own judgement.
So here is a paper for your reading.

Astrophysics > Astrophysics of Galaxies
[Submitted on 19 Oct 2022]
Forming Stars in a Dual AGN Host: Molecular and Ionized Gas in the Nearby, Luminous Infrared Merger, Mrk 266
Damien Beaulieu, Andreea Petric, Carmelle Robert, Katherine Alatalo, Timothy Heckman, Maya Merhi, Laurie Rousseau-Nepton, Kate Rowlands
We present star formation rates based on cold and ionized gas measurements of Mrk 266 (NGC 5256), a system composed of two colliding gas-rich galaxies, each hosting an active galactic nucleus. Using 12CO (1-0) observations with the Combined Array for Research in Millimeter-Wave Astronomy (CARMA), we find a total H2mass in the central region of 1.1±0.3×1010 M⊙ which leads to a possible future star formation rate of 25±10M⊙ yr−1. With the Fourier Transform Spectrograph (SITELLE) on the Canada-France-Hawaii Telescope, we measure an integrated Hα luminosity and estimate a present-day star formation rate of 15±2M⊙ yr−1 in the core of the system (avoiding the two active nuclei). These results confirm that Mrk 266 is an intermediate stage merger with a relatively high recent star formation rate and enough molecular gas to sustain it for a few hundred million years. Inflowing gas associated with the merger may have triggered both the starburst episode and two AGN but the two galaxy components differ: the region around the SW nucleus appears to be more active than the NE nucleus, which seems relatively quiet. We speculate that this difference may originate in the properties of the interstellar medium in the two systems.
Apr 13, 2021
To explain star formation on a rate that can explain Trillions of stars across Trillions of Galaxies.
Assuming Condensates over a few million solar masses are able to expel droplets of condensates that can form stars.
think of this way
1 cm droplet expanding 10^25

1000 droplets will form a cluster of stars

[Submitted on 31 Oct 2022]
The phase structure of cosmic ray driven outflows in stream fed disc galaxies
Nicolas Peschken, Michał Hanasz, Thorsten Naab, Dominik Wóltański, Artur Gawryszczak
Feeding with gas in streams is predicted to be an important galaxy growth mechanism. Using an idealised setup, we study the impact of stream feeding (with 107 M⊙ Myr−1 rate) on the star formation and outflows of disc galaxies with ∼1011 M⊙ baryonic mass. The magneto-hydrodynamical simulations are carried out with the PIERNIK code and include star formation, feedback from supernova, and cosmic ray advection and diffusion. We find that stream accretion enhances galactic star formation. Lower angular momentum streams result in more compact discs, higher star formation rates and stronger outflows. In agreement with previous studies, models including cosmic rays launch stronger outflows travelling much further into the galactic halo. Cosmic ray supported outflows are also cooler than supernova only driven outflows. With cosmic rays, the star formation is suppressed and the thermal pressure is reduced. We find evidence for two distinct outflow phases. The warm outflows have high angular momentum and stay close to the galactic disc, while the hot outflow phase has low angular momentum and escapes from the centre deep into the halo. Cosmic rays can therefore have a strong impact on galaxy evolution by removing low angular momentum, possibly metal enriched gas from the disc and injecting it into the circumgalactic medium.
Apr 13, 2021
Food for thought although, I do not agree with the paper below.
It does have merit in star formation.
I do not dispute star formation by matter collecting.
This method would take longer that the age of the predicted age of the Universe being 13.7 to 14 billion years.
Nucleosynthesis as predicted by the Big Bang theory, stars and the formation galaxies evolved from a compact source.
The process is logical to explain Nucleosynthesis of matter ejected from the core of galaxies and various cores distributed throughout the galaxies.

[Submitted on 9 Nov 2022]
Regulation of Star Formation by a Hot Circumgalactic Medium
Christopher Carr, Greg L. Bryan, Drummond B. Fielding, Viraj Pandya, Rachel S. Somerville
Galactic outflows driven by supernovae (SNe) are thought to be a powerful regulator of a galaxy's star-forming efficiency. Mass, energy, and metal outflows (ηM, ηE, and ηZ, here normalized by the star formation rate, the SNe energy and metal production rates, respectively) shape galaxy properties by both ejecting gas and metals out of the galaxy and by heating the circumgalactic medium (CGM), preventing future accretion. Traditionally, models have assumed that galaxies self-regulate by ejecting a large fraction of the gas which enters the interstellar medium (ISM), even though such high mass-loadings are in growing tension with observations. To better understand how the relative importance of ejective (i.e. high mass-loading) vs preventative (i.e. high energy-loading) feedback affects the present-day properties of galaxies, we develop a simple gas-regulator model of galaxy evolution, where the stellar mass, ISM, and CGM are modeled as distinct reservoirs which exchange mass, metals, and energy at different rates within a growing halo. Focusing on the halo mass range from 1010 to 1012M⊙, we demonstrate that, with reasonable parameter choices, we can reproduce the stellar-to-halo mass relation and the ISM-to-stellar mass relation with low mass-loaded (ηM∼0.1−10) but high energy-loaded (ηE∼0.1−1) winds, with self-regulation occurring primarily through heating and cooling of the CGM. We show that the model predictions are robust against changes to the mass-loading of outflows but are quite sensitive to our choice of the energy-loading, preferring ηE∼1 for the lowest mass halos and ∼0.1 for Milky Way-like halos.
Nov 24, 2022
Rod, firstly, I said "simple answer". There may be some newer readers happy with this, for starters. I, and many others, greatly appreciate your in depth replies. :)

Regarding uniformitarianism, I believe the correct view is to temper this with a certain (variable) amount of catastrophism. Thus, there was considerable impacting roughly 4 billion years ago. S ince the Late Heavy Bombardment, but still impacts occur from dust upwards to quite small (depending on definition).

Late Heavy Bombardment - Wikipedia › wiki › Late_Heavy_Bombard...

The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, ...
Evidence for a cataclysm · ‎Geological consequences on... · ‎Possible causes

Cat :)
I saw a programme about Mars a while ago in which they stated that the top of Mars was flatter than the remainder due to a glancing blow by a dwarf planet. This has been estimated to have been just before the late heavy bombardment of Earth. The cause of this was traced back to the ejection of millions of tons of Mars itself into space and, eventually earth. Pieces of Mars are still hitting the earth to this day. This was an accepted theory by the many experts involved in the documentary and yet some, like Brian Cox, don't even acknowledge it. One of the astronomers proudly stated that she had held a piece of Mars in her hand, found near the South Pole.
Apr 13, 2021
Bruno Mars will be proud, just joking.

We all are searching for answers to many questions.

The following paper is food for thought.

My opinion is sometimes miss-placed.

[Submitted on 22 Nov 2022]
The spatially resolved view of star formation in galaxy clusters
Bianca M. Poggianti, the GASP team
Integral field spectroscopic studies of galaxies in dense environments, such as clusters and groups of galaxies, have provided new insights for understanding how star formation proceeds, and quenches. I present the spatially resolved view of the star formation activity and its link with the multiphase gas in cluster galaxies based on MUSE and multi-wavelength data of the GASP survey. I discuss the link among the different scales (i.e. the link between the spatially resolved and the global star formation rate-stellar mass relation), the spatially resolved signatures and the quenching histories of jellyfish (progenitors) and post-starburst (descendants) galaxies in clusters. Finally, I discuss the multi-wavelength view of star-forming clumps both in galaxy disks and in the tails of stripped gas.


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