Galaxies all spin ~ 1 rotation per billion years

March 16, 2018, 03:09 PM

feersum dreadnaught

Just in case you needed to set your watch...

Cosmic clocks: A Tight Radius - Velocity Relationship for HI-Selected Galaxies

HI-Selected galaxies obey a linear relationship between their maximum detected radius Rmax and rotational velocity. This result covers measurements in the optical, ultraviolet, and HI emission in galaxies spanning a factor of 30 in size and velocity, from small dwarf irregulars to the largest spirals. Hence, galaxies behave as clocks, rotating once a Gyr at the very outskirts
of their discs. Observations of a large optically-selected sample are consistent, implying this relationship is generic to disc galaxies in the low redshift Universe. A linear RV relationship
is expected from simple models of galaxy formation and evolution. The total mass within Rmax has collapsed by a factor of 37 compared to the present mean density of the Universe.

Adopting standard assumptions we find a mean halo spin parameter λ in the range 0.020 to 0.035. The dispersion in λ, 0.16 dex, is smaller than expected from simulations. This may be
due to the biases in our selection of disc galaxies rather than all halos. The estimated mass densities of stars and atomic gas at Rmax are similar (∼ 0.5 M pc−2) indicating outer discs
are highly evolved. The gas consumption and stellar population build time-scales are hundreds of Gyr, hence star formation is not driving the current evolution of outer discs. The estimated ratio between Rmax and disc scale length is consistent with long-standing predictions from monolithic collapse models. Hence, it remains unclear whether disc extent results from continual accretion, a rapid initial collapse, secular evolution or a combination thereof.

http://s3-ap-southeast-2.amazo...mic-Clocks-Paper.pdf

March 16, 2018, 03:14 PM

fiasconva

Does this finally explain why we switched to daylight saving time? *s*

March 16, 2018, 03:16 PM

Balzé Halzé

quote:
Originally posted by feersum dreadnaught:

Adopting standard assumptions we find a mean halo spin parameter λ in the range 0.020 to 0.035. The dispersion in λ, 0.16 dex, is smaller than expected from simulations. This may be due to the biases in our selection of disc galaxies rather than all halos. The estimated mass densities of stars and atomic gas at Rmax are similar (∼ 0.5 M pc−2) indicating outer discs are highly evolved.

Well duh.

March 16, 2018, 03:27 PM

preten2b

Wow, that is a... er... well over my head.

Or does this explain slow Amazon shipping?

March 16, 2018, 03:28 PM

sigmonkey

It has something to do with the Toyota Corolla FX.

March 16, 2018, 03:30 PM

parabellum

Look up 'The Anthropic Principle'

March 16, 2018, 03:48 PM

tacfoley

quote:
Originally posted by feersum dreadnaught:
Just in case you needed to set your watch...

Cosmic clocks: A Tight Radius - Velocity Relationship for HI-Selected Galaxies

HI-Selected galaxies obey a linear relationship between their maximum detected radius Rmax and rotational velocity. This result covers measurements in the optical, ultraviolet, and HI emission in galaxies spanning a factor of 30 in size and velocity, from small dwarf irregulars to the largest spirals. Hence, galaxies behave as clocks, rotating once a Gyr at the very outskirts
of their discs. Observations of a large optically-selected sample are consistent, implying this relationship is generic to disc galaxies in the low redshift Universe. A linear RV relationship
is expected from simple models of galaxy formation and evolution. The total mass within Rmax has collapsed by a factor of 37 compared to the present mean density of the Universe.

Adopting standard assumptions we find a mean halo spin parameter λ in the range 0.020 to 0.035. The dispersion in λ, 0.16 dex, is smaller than expected from simulations. This may be
due to the biases in our selection of disc galaxies rather than all halos. The estimated mass densities of stars and atomic gas at Rmax are similar (∼ 0.5 M pc−2) indicating outer discs
are highly evolved. The gas consumption and stellar population build time-scales are hundreds of Gyr, hence star formation is not driving the current evolution of outer discs. The estimated ratio between Rmax and disc scale length is consistent with long-standing predictions from monolithic collapse models. Hence, it remains unclear whether disc extent results from continual accretion, a rapid initial collapse, secular evolution or a combination thereof.

http://s3-ap-southeast-2.amazo...mic-Clocks-Paper.pdf

See you around....

tac

March 16, 2018, 03:59 PM

Scoutmaster

quote:
Originally posted by parabellum:
Look up 'The Anthropic Principle'

I hadn't seen that before, it makes sense.

A noted scientist once asked me "how much science was true 50 years ago that today we know is false -- and, how much science is considered true today that in 50 years we will know is false?" After the 1994 Northridge (CA) earthquake, the USGS acknowleded their seismic models re CA were wrong, the earth didn't do what it was supposed to do.

A couple of years ago a science article noted that three deep space observation telescopes detected/recorded the same highly unexpected phenomenon out in the galaxy. They compared data and analysis, got the same results. The outcome was that if the speed of light can exceed the speed of light, everything fits, "but we are not going to go there".