Astronomy

Primordial angular momentum?

Primordial angular momentum?


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Angular momentum, and in particular the conservation of angular momentum, is of course very relevant in many processes in astrophysics, such as e.g. star- and planet formation, and disk formation in galaxies.

The concept of objects spinning up upon collapse is straightforward enough to understand, but this begs the question: where does the primordial angular momentum come from?

Tidal interactions between haloes, I suppose?


Your hypothesis is correct: it is the tidal interaction between neighbours which generates spin.

Think of your proto halo (galaxy, stellar disc etc) as an ellipsoid (set by it's inertial tensor). Should the matter around it not be spherically distributed, it will apply a torque onto that ellipsoid and make it spin. The assumption in cosmology is that even though the primordial angular momentum you mention may be null, tidal interaction between neighbouring proto structures is sufficient to allow then to exchange (hence acquire individually) angular momentum, while preserving a zero sum.

A Reference on this subject is given by this paper

This diagram may enlighten the issue: it represents the tidal torquing of the blue ellipsoid by the tides represented by the pink ellipsoid.

PS: the expression spin up is unfortunate it seems because it is in fact spin conservation at the later stage of collapse of the proto halo which makes it rotate faster while preserving it spin (= total internal angular momentum).


Let's say I'm floating in space with two toy tops. I spin them in opposite directions at the same speed. Each of them has angular momentum but the total angular momentum of the system is zero.

On a larger scale the same thing could happen universe-wide. As stars and galaxies formed they would end up spinning every which way, but the total angular momentum would be unchanged.


Scientists discover largest rotating structures in the universe

Artist’s impression of cosmic filaments: huge bridges of galaxies and dark matter connect clusters of galaxies to each other. Galaxies are funnelled on corkscrew like orbits towards and into large clusters that sit at their ends. Their light appears blue-shifted when they move towards us, and red-shifted when they move away. (Credit: AIP/ A. Khalatyan/ J. Fohlmeister) Photograph:( Others )

Story highlights

The results published in Nature Astronomy signify that angular momentum can be generated on unprecedented scales

Astronomers have discovered the largest rotating structures in the Universe by mapping the motion of galaxies in huge filaments that connect the cosmic web.

These long tendrils of galaxies spin on the scale of hundreds of millions of light-years. A rotation on such enormous scales has never been seen before according to astronomers at the Leibniz Institute for Astrophysics Potsdam (AIP).

The results published in Nature Astronomy signify that angular momentum can be generated on unprecedented scales.

Such a potential flow is irrotational or curl-free: there is no primordial rotation in the early Universe and angular momentum must be generated as structures form.

Cosmic filaments are huge bridges of galaxies and dark matter that connect clusters of galaxies to each other. They funnel galaxies towards and into large clusters that sit at their ends.

According to Peng Wang, both an author of the study and astronomer at the AIP, “By mapping the motion of galaxies in these huge cosmic superhighways using the Sloan Digital Sky survey – a survey of hundreds of thousands of galaxies – we found a remarkable property of these filaments: they spin.”

“Despite being thin cylinders – similar in dimension to pencils – hundreds of millions of light-years long, but just a few million light-years in diameter, these fantastic tendrils of matter rotate,” adds Noam Libeskind, initiator of the project at the AIP.

“On these scales the galaxies within them are themselves just specs of dust. They move on helixes or corkscrew-like orbits, circling around the middle of the filament while travelling along with it. Such a spin has never been seen before on such enormous scales, and the implication is that there must be an as yet unknown physical mechanism responsible for torquing these objects.”

How the angular momentum responsible for the rotation is generated in a cosmological context is one of the key unsolved problems of cosmology. In the standard model of structure formation, small overdensities present in the early universe grow via gravitational instability as matter flows from under to overdense regions.

Such a potential flow is irrotational or curl-free: there is no primordial rotation in the early universe. As such any rotation must be generated as structures form. The cosmic web in general and filaments, in particular, are intimately connected with galaxy formation and evolution. They also have a strong effect on galaxy spin, often regulating the direction of how galaxies and their dark matter halos rotate. However, it is not known whether the current understanding of structure formation predicts that filaments themselves, being uncollapsed quasi-linear objects, should spin.

“Motivated by the suggestion from the theorist Dr Mark Neyrinck that filaments may spin, we examined the observed galaxy distribution, looking for filament rotation,” says Noam Libeskind. “It's fantastic to see this confirmation that intergalactic filaments rotate in the real Universe, as well as in computer simulation.”

By using a sophisticated mapping method, the observed galaxy distribution was segmented into filaments. Each filament was approximated by a cylinder. Galaxies within it were divided into two regions on either side of the filament spine (in projection) and the mean redshift difference between the two regions was carefully measured.

The mean redshift difference is a proxy for the velocity difference (the Doppler shift) between galaxies on the receding and approaching side of the filament tube. It can thus measure the filament’s rotation. The study implies that depending on the viewing angle and end point mass, filaments in the universe show a clear signal consistent with rotation.


Angular momentum loss of primordial gas in Lyα radiation field

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Research output : Contribution to journal › Article › peer-review

T1 - Angular momentum loss of primordial gas in Lyα radiation field

N2 - We present results on the radiation drag exerted by an isotropic and homogeneous background of Lyα photons on neutral gas clouds orbiting within H II regions around Population III stars of different masses. The Doppler shift causes a frequency difference between photons moving in the direction of the cloud and opposite to it resulting in a net momentum loss of the cloud in the direction of motion. We find that half of the angular momentum of gas with vθ ≲ 20 km s-1 near (r ≲ 3 kpc) a Population III star of 120 M⊙ at z = 20 is lost within ˜106 yr. The radiation drag is a strong function of cloud velocity that peaks at v ˜ 20 km s-1 reflecting the frequency dependence of the photon cross-section. Clouds moving with velocities larger than ˜100 km s-1 lose their angular momentum on time-scales of ˜108 yr. At lower redshifts radiation drag becomes inefficient as the Lyα photon density in H II regions decreases by a factor (1 + z)3 and angular momentum is lost on time-scales ≳ 108 yr even for low-velocity clouds. Our results suggest that a sweet spot exists for the loss of angular momentum by radiation drag for gas clouds at z > 10 and with v ˜ 20 km s-1. Comparison to dynamical friction forces acting on typical gas clouds suggest that radiation drag is the dominant effect impacting the orbit. We propose that this effect can suppress the formation of extended gas discs in the first galaxies and help gas accretion near galactic centres and central black holes.

AB - We present results on the radiation drag exerted by an isotropic and homogeneous background of Lyα photons on neutral gas clouds orbiting within H II regions around Population III stars of different masses. The Doppler shift causes a frequency difference between photons moving in the direction of the cloud and opposite to it resulting in a net momentum loss of the cloud in the direction of motion. We find that half of the angular momentum of gas with vθ ≲ 20 km s-1 near (r ≲ 3 kpc) a Population III star of 120 M⊙ at z = 20 is lost within ˜106 yr. The radiation drag is a strong function of cloud velocity that peaks at v ˜ 20 km s-1 reflecting the frequency dependence of the photon cross-section. Clouds moving with velocities larger than ˜100 km s-1 lose their angular momentum on time-scales of ˜108 yr. At lower redshifts radiation drag becomes inefficient as the Lyα photon density in H II regions decreases by a factor (1 + z)3 and angular momentum is lost on time-scales ≳ 108 yr even for low-velocity clouds. Our results suggest that a sweet spot exists for the loss of angular momentum by radiation drag for gas clouds at z > 10 and with v ˜ 20 km s-1. Comparison to dynamical friction forces acting on typical gas clouds suggest that radiation drag is the dominant effect impacting the orbit. We propose that this effect can suppress the formation of extended gas discs in the first galaxies and help gas accretion near galactic centres and central black holes.


Cosmic Order out of Primordial Chaos: A tribute to Nikos Voglis

Chaos in Astronomy.: Astrophysics and Space Science Proceedings. ed. / G. Contopoulos G. P. Patsis . Berlin : Springer, 2008. p. 467-483 ( Astrophysics and Space Science Proceedings ).

Research output : Chapter in Book/Report/Conference proceeding › Chapter › Academic › peer-review

T1 - Cosmic Order out of Primordial Chaos

T2 - A tribute to Nikos Voglis

AU - van de Weijgaert, Marinus

N1 - Relation: http://www.rug.nl/ date_submitted:2008 Rights: University of Groningen

N2 - Nikos Voglis had many astronomical interests, among them was the question of the origin of galactic angular momentum. In this short tribute we review how this subject has changed since the 1970’s and how it has now become evident that gravitational tidal forces have not only caused galaxies to rotate, but have also acted to shape the very cosmic structure in which those galaxies are found. We present recent evidence for this based on data analysis techniques that provide objective catalogues of clusters, filaments and voids.

AB - Nikos Voglis had many astronomical interests, among them was the question of the origin of galactic angular momentum. In this short tribute we review how this subject has changed since the 1970’s and how it has now become evident that gravitational tidal forces have not only caused galaxies to rotate, but have also acted to shape the very cosmic structure in which those galaxies are found. We present recent evidence for this based on data analysis techniques that provide objective catalogues of clusters, filaments and voids.


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Primordial angular momentum? - Astronomy

100 until the first minihalo forms. Once the gas infalls toward the center of the minihalo and condenses, we implement the 'sink particle' method to represent regions that will form a star, and we follow the evolution of the metal-free, star-forming gas for many free-fall times. A disk forms around the initial Pop III star and fragments to form secondary stars with a range of masses (1 - 50 [solar mass]). This is markedly different from the previous paradigm of one single, massive star forming per minihalo. Using a ray-tracing technique, we also examine the effect of radiative feedback on protostellar growth and disk fragmentation. This feedback will not prevent the formation of secondary stars within the disk, but will reduce the final mass reached by the largest Pop III star. Measuring the angular momentum of the gas that falls onto the sink regions, we also find that the more massive Pop III stars accrete sufficient angular momentum to rotate at nearly break-up speeds, and can potentially end their lives as collapsar gamma-ray bursts or hypernovae. We furthermore numerically examine the recently discovered relative streaming motions between dark matter and baryons, originating from the era of recombination. Relative streaming will slightly delay the redshift at which Pop III stars first form, but will otherwise have little impact on Pop III star formation and the history of reionization. We finally evaluate the possible effect of a cosmic ray (CR) background generated by the supernova deaths of massive Pop III stars. A sufficiently large CR background could indirectly enhance the H₂ cooling within the affected minihalos. The resulting lower temperatures would lead to a reduced characteristic stellar mass (

10 [solar mass]), providing another possible pathway to form low-mass Pop III stars.


Primordial angular momentum? - Astronomy

Chiral symmetry is maximally violated in weak interactions [1], and such microscopic asymmetries in the early Universe might leave observable imprints on astrophysical scales without violating the cosmological principle. In this Letter, we propose a helicity measurement to detect primordial chiral violation. We point out that observations of halo-galaxy angular momentum directions (spins), which are frozen in during the galaxy formation process, provide a fossil chiral observable. From the clustering mode of large scale structure of the Universe, we construct a spin mode in Lagrangian space and show in simulations that it is a good probe of halo-galaxy spins. In the standard model, a strong symmetric correlation between the left and right helical components of this spin mode and galaxy spins is expected. Measurements of these correlations will be sensitive to chiral breaking, providing a direct test of chiral symmetry breaking in the early Universe.

© 2020 American Physical Society

Physics Subject Headings (PhySH)

Authors & Affiliations

  • 1 Department of Astronomy, Xiamen University, Xiamen, Fujian 361005, China
  • 2 Canadian Institute for Theoretical Astrophysics, University of Toronto, M5S 3H8, Ontario, Canada
  • 3 Tsung-Dao Lee Institute, Shanghai Jiao Tong University, Shanghai, 200240, China
  • 4 Dunlap Institute for Astronomy and Astrophysics, University of Toronto, M5S 3H4, Ontario, Canada
  • 5 Canadian Institute for Advanced Research, CIFAR Program in Gravitation and Cosmology, Toronto, M5G 1Z8, Ontario, Canada
  • 6 Perimeter Institute for Theoretical Physics, Waterloo, N2L 2Y5, Ontario, Canada
  • 7 Department of Astronomy, Shanghai Jiao Tong University, Shanghai, 200240, China
  • 8 Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026, China
  • 9 Tsinghua Center of Astrophysics & Department of Physics, Tsinghua University, Beijing, 100084, China
  • 10 Department of Astronomy, University of Massachusetts Amherst, Massachusetts 01003, USA

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Angular momentum distribution during the collapse of primordial star-forming clouds

It is generally believed that angular momentum is distributed during the gravitational collapse of the primordial star forming cloud. However, so far there has been little understanding of the exact details of the distribution. We use the modified version of the Gadget-2 code, a three-dimensional smoothed-particle hydrodynamics simulation, to follow the evolution of the collapsing gas in both idealized as well as more realistic minihalos. We find that, despite the lack of any initial turbulence and magnetic fields in the clouds the angular momentum profile follows the same characteristic power-law that has been reported in studies that employed fully self-consistent cosmological initial conditions. The fit of the power-law appears to be roughly constant regardless of the initial rotation of the cloud. We conclude that the specific angular momentum of the self-gravitating rotating gas in the primordial minihalos maintains a scaling relation with the gas mass as (L propto M^<1.125>) . We also discuss the plausible mechanisms for the power-law distribution.

This is a preview of subscription content, access via your institution.


WIMPs vs. MACHOs

To understand the drive behind finding PBHs comes from trying to understand if dark matter is made of WIMPs (Weakly Interacting Massive Particles) or MACHOs (Massive Compact Halo Objects), both unproven concepts. But something that already has lots of evidence in its favor are black holes, and they have many characteristics that MACHOs would have. But, and this is key, some more properties would be needed if they were to be MACHO candidates such as a certain galactic distribution, patterns in the cosmic web, and gravitational lensing effects, all of which we haven’t seen yet. Nothing so far has yielded the expected MACHO response, and so they are no longer a major candidate for dark matter. But don’t confuse that with scientists giving up on them. They have conducted a microgravity lensing observation to try and place some limits on the mass of these objects. After such a search in the Small Magellanic Cloud, no MACHO candidates were spotted and so scientists knew from that data that the largest MACHO could be 10 solar masses but expect them to be much smaller than that. Naturally, scientists moved on and looked for WIMPs, but that search has gained more attention and yet equally lacking results as its counterpart. Some models predict PBHs could be WIMP factories via Hawking radiation considerations, for size is inversely correlated to temperature. Therefore, a small object like a PBH should be very hot, therefore radiative. If WIMPs exist, then collisions between them should create a distinctive gamma ray that is yet unseen. So now the spotlight is once again on MACHOs, for there is a type of black hole that would be a perfect MACHO candidate: a PBH. Hard to see yet offering the gravitational pull needed, they would be a great target (Garcia 40, BEC, Rzetelny, Crane 40).


A primordial origin for misalignments between stellar spin axes and planetary orbits

The existence of gaseous giant planets whose orbits lie close to their host stars ('hot Jupiters') can largely be accounted for by planetary migration associated with viscous evolution of proto-planetary nebulae. Recently, observations of the Rossiter-McLaughlin effect during planetary transits have revealed that a considerable fraction of hot Jupiters are on orbits that are misaligned with respect to the spin axes of their host stars. This observation has cast doubt on the importance of disk-driven migration as a mechanism for producing hot Jupiters. Here I show that misaligned orbits can be a natural consequence of disk migration in binary systems whose orbital plane is uncorrelated with the spin axes of the individual stars. The gravitational torques arising from the dynamical evolution of idealized proto-planetary disks under perturbations from massive distant bodies act to misalign the orbital planes of the disks relative to the spin poles of their host stars. As a result, I suggest that in the absence of strong coupling between the angular momentum of the disk and that of the host star, or of sufficient dissipation that acts to realign the stellar spin axis and the planetary orbits, the fraction of planetary systems (including systems of 'hot Neptunes' and 'super-Earths') whose angular momentum vectors are misaligned with respect to their host stars will be commensurate with the rate of primordial stellar multiplicity.


Watch the video: Dimentionless Angular Momentum (November 2022).