It was in 1929 that Edwin Hubble formulated a key principle about the universe. Hubble realized that the redshift of distant galaxies was proportional to their distance, and refinements to the Hubble constant have brought some sense of order to our view of the expanding cosmos ever since. But an Ohio State astronomer and his colleagues now argue for tweaking Hubble, to the tune of 15 percent. That’s the difference between previous readings of the distance to M33, the Triangulum Galaxy, and the value they have recently measured.
The paper by Kris Stanek and co-authors is slated for the Astrophysical Journal, and is available in preprint form here. In it, the team describes its study of M33 in optical and infrared wavelengths using a wide variety of instruments including the 10-meter telescopes at Hawaii’s Keck Observatory. The work on an eclipsing binary system in M33 produced a measurement of 3 million light years from Earth for the galaxy as opposed to the 2.6 million as determined by the Hubble constant. That would imply a larger universe than previously thought.
Image: M33, the Triangulum Galaxy. Credit: ASA/JPL-Caltech/GALEX.
“Our margin of error is now 6 percent, which is actually pretty good,” Stanek says. But it will take further calculations based on another stellar system in M33 to reduce the error further, or perhaps observations of the nearby Andromeda galaxy. And because eclipsing binaries in the right settings are uncommon, we’re talking two more years of meaurements to produce the needed follow-up.
I think you mean the ‘visible’ universe… We see a sphere about 15Gy in radius, because light from objects farther away hasn’t had time to reach us… But that does not mean that if we were to go over ‘that’ way 5G light-years we’d see the edge 10Gy away. We’d still see a sphere of 15Gy radius. No-one knows how big the universe is. It may be infinite. It may curve back on itself.
…and, don’t forget, it is probably expanding quite rapidly
Yes, and that expansion continues to challenge what we know about the makeup of what we see (and even more important, what we don’t see). Good points above re nomenclature, especially re the ‘visible’ universe.
Wow! Looks like Alan Sandage et. al. were right with their low Ho values. Wonder what systematic errors the HST survey has that produced a higher Ho? Are there no appropriate eclipsing binaries in the Magellanic clouds that also could be used for a more local Cephied distance yardstick comparison? Hopefully, others will soon work to reproduce or refute these surprising measurements.
One important thing to remember about cosmic distances is that while the starlight has travelled for 15 gigayears the Universe has expanded. The physical distance to a source ’15 gigayears’ distant is dependent on the cosmological model used, so in a flat Universe the distance is about 3 times the light-travel time. So the ‘edge’ of the visible Universe is currently 45 giga-lightyears distant.
If the Universe is slightly closed then the distance to the furtherest point is pi*L-h/sqrt(Omega-o – 1), L-h being the Hubble distance, Omega-o is the density parameter. Current data suggests Omega-o is about 1.01-1.02, thus the opposite side of the Universe is 430 to 304 gigalightyears away. Thus we see about 0.058% to less than 0.2% of the Universe.
And no doubt Alan Sandage would be well pleased with the low H-o result.
Hubble’s Cosmology: From a Finite Expanding Universe to a Static Endless Universe
Authors: A.K.T. Assis (Institute of Physics `Gleb Wataghin’ University of Campinas, Brazil), M.C.D. Neves (Departamento de Física, Fundação Universidade Estadual de Maringá, Brazil), D.S.L. Soares (Departamento de Física, ICEx, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil)
(Submitted on 27 Jun 2008)
Abstract: We analyze Hubble’s approach to cosmology. In 1929 he accepted a finite expanding universe in order to explain the redshifts of distant galaxies. Later on he turned to an infinite stationary universe due to observational constraints. We show, by quoting his works, that he remained cautiously against the big bang until the end of his life.
Comments: Paper accepted for presentation at the Second Crisis in Cosmology Conference, to be held on 2008 September 7-11, Port Angeles, Washington, USA
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0806.4481v1 [astro-ph]
Submission history
From: Domingos Soares [view email]
[v1] Fri, 27 Jun 2008 10:41:32 GMT (15kb)
http://arxiv.org/abs/0806.4481
I remember reading this here but it doesn’t seem like nearly 3 years ago. Wow!
Few in cosmology, as of June 009, are still trying to precisely determine the Hubble constant because few today believe it is a constant. They have claimed both accelerated expansion, and most recently decelerated expansion before that.
I believe neither are true and that their equation for calculating distances, the Hubble formula, needs adjustment. That’s not all. The standard model I believe is also on its way out because of all the distant fully formed giant galaxies they have been finding supposedly at the edge of time. Unfortunately I’ve been predicting the fall of the BB model since the 60’s.
As for M33, they should find that all galaxies with a redshift of .68 (about 2,000 Mpc) or less have been underestimated as far as their distances and sizes, and for galaxies farther away than that, distances and sizes are overestimated.
Sorry, no Hubble constant — not even an expanding universe for that matter — at least that’s my take on it.
PAndAS’ cubs: discovery of two new dwarf galaxies in the surroundings of the Andromeda and Triangulum galaxies
Authors: Nicolas F. Martin, Alan W. McConnachie, Mike Irwin, Lawrence M. Widrow, Annette M. N. Ferguson, Rodrigo A. Ibata, John Dubinski, Arif Babul, Scott Chapman, Mark Fardal, Geraint F. Lewis, Julio Navarro, R. Michael Rich
(Submitted on 2 Sep 2009 (v1), last revised 9 Sep 2009 (this version, v2))
Abstract: We present the discovery of two new dwarf galaxies, Andromeda XXI and Andromeda XXII, located in the surroundings of the Andromeda and Triangulum galaxies (M31 and M33). These discoveries stem from the first year data of the Pan-Andromeda Archaeological Survey (PAndAS), a photometric survey of the M31/M33 group conducted with the Megaprime/MegaCam wide-field camera mounted on the Canada-France-Hawaii Telescope.
Both satellites appear as spatial overdensities of stars which, when plotted in a color-magnitude diagram, follow metal-poor, [Fe/H]=-1.8, red giant branches at the distance of M31/M33. Andromeda XXI is a moderately bright dwarf galaxy (M_V=-9.9+/-0.6), albeit with low surface brightness, emphasizing again that many relatively luminous M31 satellites still remain to be discovered. It is also a large satellite, with a half-light radius close to 1 kpc, making it the fourth largest Local Group dwarf spheroidal galaxy after the recently discovered Andromeda XIX, Andromeda II and Sagittarius around the Milky Way, and supports the trend that M31 satellites are larger than their Milky Way counterparts.
Andromeda XXII is much fainter (M_V=-6.5+/-0.8) and lies a lot closer in projection to M33 than it does to M31 (42 vs. 224 kpc), suggesting that it could be the first Triangulum satellite to be discovered. Although this is a very exciting possibility in the context of a past interaction of M33 with M31 and the fate of its satellite system, a confirmation will have to await a good distance estimate to confirm its physical proximity to M33.
Along with the dwarf galaxies found in previous surveys of the M31 surroundings, these two new satellites bring the number of dwarf spheroidal galaxies in this region to 20.
Comments: 10 pages, 6 figures, accepted for publication in ApJ; v2: minor typographical corrections
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:0909.0399v2 [astro-ph.CO]
Submission history
From: Nicolas Martin [view email]
[v1] Wed, 2 Sep 2009 11:50:47 GMT (150kb)
[v2] Wed, 9 Sep 2009 14:46:49 GMT (150kb)
http://arxiv.org/abs/0909.0399