Questions extracted from EPoS research with the aim to identify a set of "big questions"
Definition: which evolutionary phase is meant?
The early phase ranges from the assembly of a molecular cloud to proto-stars surrounded by accreting matter, e.g. in form of a disk. Later phases when the stars has almost finished accretion and may be surrounded by a proto-planetary disks are excluded.
Source
The questions are gathered from published reviews and papers, presentations, and discussions. Names and citations are intentionally not given to keep personal biases out.
Definition: what means "big"?
Without answering a "big" question it is not possible to explain the early phase SF process. In the EPoS field, the entangled action of many physical processes makes the application of this definition especially difficult. A substantial fraction of the listed questions may actually turn out to be not a "big" question.
Highly disputed
Since research funding is favorably provided for break-through achievements in the big questions of a field, their precise content is a matter of intense scientific and science-political discussion. Persons might claim that some of the questions already have been answered.
Input to this list
If you have a comment about this list, a paper or pdf with potentially big questions not mentioned here, a request to change wording, or a wish to add a question, you can send it as email to steinmpiade.
Last change: 03 May 2024 13:12 CET     (83 questions)
Abbreviations: SF=star formation, (G)MC=(giant) molecular cloud, IRDC=infrared dark cloud

G e n e r a l
Ge01
Are low-mass stars formed by a different physical process than high-mass stars?
Ge02
Fi03
Does early phase SF have important length scales?
Ge03
What is the fraction of stars being formed by triggered SF?
Ge04
What is the fraction of high-mass stars that evolve through stellar merging?
Ge05
What regulates the SF efficiency/rate?
Ge06
Is there a sequence in the SF process in which low-mass SF, high-mass SF, and feedback act in a certain order?
Ge07
In which phase is the SF process considerably affected by cosmic rays?
Ge08
In which phase and by which physical processes is the multiplicity of newly-formed stars determined?
Ge09
Can radiation stop accretion?
Ge10
What is the main driver of the turbulence that is affecting SF regions?
Ge11
Is there a limit for the final mass of the formed star and how does it depend on the metallicity in the forming cloud?
Ge12
What is the origin of the initial mass functions measured in different locations of the Galaxy?
Ge13
From the molecular cloud down to the inner border of an accretion disk, where are the regions that are magnetically dominated?
Ge14
Is there a global column density limit for SF to start?
Ge15
At what scale does turbulence influence material and what is its effect?
Ge16
Will the numerically difficult inclusion of realistic (magnetic) turbulence on all scales change existing models of SF?
Ge17
Does ambipolar diffusion have a measurable effect on SF?
Ge18
What mechanism solves the angular momentum problem at MC scales?
Ge19
How does the evolving protostar affect the matter accreting on it?
Ge20
Which effects hinder or terminate SF leading to the observed low Galactic SF efficiencies?
Ge21
Does the formation and destruction of molecular ices play any role in the early SF process?
Ge22
How do the properties of MC and the SF in their interior depend on galactic environment?
Ge23
What is the role of metallicity both in the SF process and in conversions from observations to properties?
Ge24
What are the cosmic dust properties in the SF regions and how does our limited knowledge about them hinder us to derive physical quantities?

M o l e c u l a r   C l o u d s
MC01
Which processes form the MCs?
MC02
Fi01
Which processes are responsible for the observed filamentary structure of MCs?
MC03
What are the timescales for the formation of the MC, its filamentary structure, the cores, and the MC destruction, and how are they related?
MC04
Gravity, magnetic fields, radiation, and turbulence are considered to impact the formation and evolution of MCs. When and how?
MC05
In view of galaxies without spiral arms showing GMCs/SF, are spiral arms necessary to form MCs?
MC06
How much do the conditions to form MCs change near the Galactic center compared to the disk, and how much is that reflected in their properties?
MC07
Fe04
What effect has the feedback within one MC on another MC (e.g. during its destruction)?
MC08
Are MCs in static virial equilibrium?
MC09
How much gas can a dense region in a GMC accumulate before SF starts?
MC10
What is the fraction of MCs that undergo gravitational collapse?
MC11
Do all GMCs form stars?
MC12
What is the role of the Galaxy in both forming and destroying MCs?

F i l a m e n t s
Fi01
MC02
Which processes are responsible for the observed filamentary structure of MCs?
Fi02
What causes the fibers in filaments?
Fi03
Ge02
Do filaments have a universal thickness related to the Jeans mass?
Fi04
Co01
What causes the appearance of cores in filaments?
Fi05
What fragments filaments?
Fi06
Is the mass flow through converging filaments the dominant process to form clusters?
Fi07
What determines the lifetime of a filament?
Fi08
Do all filaments have fibers?
Fi09
How essential for the filament mass and evolution is the mass supply by striation?
Fi10
Are magnetic fields affecting the filament evolution?
Fi11
Is there a relation between the filament properties and the core properties?
Fi12
Co12
Are there cores that have not formed in a filament?
Fi13
Is the formation of dense clumps at the end of filaments (EDC, end-dominated filaments) a common process?
Fi14
Can the properties of future cores already be deduced from the filament properties?
Fi15
How do filaments accrete from their surrounding and which forces aside of gravitation affect this accretion?
Fi16
Fe05
Is the feedback of a massive star/cluster able to form filamentary structures in a nearby dense region?
Fi17
Co16
What are the precise physical differences between filaments/clumps/fragments/cores?

C o r e s
Co01
Fi04
What causes the appearance of cores in filaments?
Co02
Which processes stabilize the core?
Co03
What causes the core collapse?
Co04
Why does turbulence weaken towards the center of the cores?
Co05
How strong is the effect of non-ideal MHD effects on the evolution of the core (influencing the importance of ionization processes in the core)?
Co06
How important is core collision in the overall math of SF?
Co07
Is there a relation between the core properties and the properties of the created stellar population?
Co08
Is it possible to destroy cores (e.g. by large-scale shearing motions) before they can create a star?
Co09
Are there high-mass pre-stellar cores?
Co10
How does the combined action of competitive accretion and fragmentation lead to the observed variety in core mass functions?
Co11
Do cores already show mass segregation within young stellar clusters?
Co12
Fi12
Are there cores that have not formed in a filament?
Co13
Fe03
Cores near a forming cluster: will the radiation and winds trigger SF or prevent it?
Co14
Do all cores (even in IRDCs) start as a low-mass core with about a thermal Jeans mass and then grow by competitive accretion?
Co15
Is the core collapse in quasi-equilibrium or a pressureless free-fall?
Co16
Fi17
What are the precise physical differences between filaments/clumps/fragments/cores?

D i s k s
Di01
Do all stars have a phase where they accrete mass through a circumstellar disk?
Di02
Which physical mechanisms provide viscosity in the disk aiding to accrete matter onto the star?
Di03
Je03
How much of the angular momentum of the disks is removed by the jet and the outflow?
Di04
Which process accretes more mass onto the star: accretion events or low-rate constant accretion?
Di05
Are there extended massive disks around proto-stars?
Di06
How much mass is accreted through disk-instabilities?
Di07
How common are accretion streamers?
Di08
How much is the disk disturbed by the infall through streamers?
Di09
Is protostellar disk formation regulated magnetically?
Di10
Does planet formation take place in protostellar disks already?

J e t s / O u t f l o w s
Je01
Which mechanisms launch the jet and the outflow from the star-disk system?
Je02
What mechanism collimates the jet?
Je03
Di03
How much of the angular momentum of the disk/star system is removed by the jet and the outflow?
Je04
How much turbulence is injected by the jets and the outflows into the SF region?
Je05
What is causing explosive outflows?
Je06
Are the jet knots created by pulsed injection or interaction with the ambient medium?
Je07
Why are jets observed only in a small fraction of the lifetime of the disk?

F e e d b a c k
Fe01
How do the radiation, heat transfer, winds, (turbulent) flows, cosmic rays, and MHD/plasma waves produced during the SF process affect the SF in the region?
Fe02
In low-mass SF regions without a strong radiation field and SN shocks, which feedback process dominates (e.g., jets, outflows, stellar winds, turbulence, cosmic rays, etc.)?
Fe03
Co13
Cores near a forming cluster: will the radiation and winds trigger SF or prevent it?
Fe04
MC07
What effect has the feedback within one MC on another MC (e.g. during its destruction)?
Fe05
Fi16
Is the feedback of a massive star/cluster able to form filamentary structures in a nearby dense region?
Fe06
Can the numerous B stars compete with their wind feedback against the strong feedback of a few SNs?
The end is near!