Hubble bubble (astronomy)

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The Hubble Space Telescope reveals many local anomalies in the generally homogeneous character of interstellar space, such as this galaxy (NGC 4526) and the supernova beside it (SN 1994D). SN1994D.jpg
The Hubble Space Telescope reveals many local anomalies in the generally homogeneous character of interstellar space, such as this galaxy (NGC 4526) and the supernova beside it (SN 1994D).

In astronomy, a Hubble bubble would be "a departure of the local value of the Hubble constant from its globally averaged value," [1] or, more technically, "a local monopole in the peculiar velocity field, perhaps caused by a local void in the mass density." [2]

Contents

The Hubble constant, named for astronomer Edwin Hubble, whose work made clear the expansion of the universe, measures the rate at which expansion occurs. In accordance with the Copernican principle that the Earth is not in a central, specially favored position, one would expect that measuring this constant at any point in the universe would yield the same value. If, on the other hand, Earth were at or near the center of a very low-density region of interstellar space (a relative void), the local expansion would be faster due to the lack of nearby mass to slow it down. Thus, stars inside such a "Hubble bubble" would accelerate away from Earth faster than the general expansion of the universe. [1] [3] This situation could provide an alternative to dark energy in explaining the apparent accelerating universe [3] or contribute to explanations of the Hubble tension. [4] [5]

Hubble bubble proposed

In 1998, Zehavi et al. reported evidence in support of a Hubble bubble. [6] The initial suggestion that local redshift velocities differ from those seen elsewhere in the universe was based on observations of Type Ia supernovae, often abbreviated "SNe Ia." Such stars have been used as standard candle distance markers for 20 years, and were key to the first observations of dark energy. [7]

Zehavi et al. studied the peculiar velocities of 44 SNe Ia to test for a local void, and reported that Earth seemed to be inside a relative void of roughly 20% underdensity, surrounded by a dense shell, a "bubble". [6]

Testing the hypothesis

In 2007, Conley et al. examined the SNe Ia color data comparisons while taking into account the effect of cosmic dust in external galaxies. They concluded that the data did not support the existence of a local Hubble bubble. [2]

In 2010, Moss et al. analyzed the Hubble Bubble model although without using that name, [1] saying "The suggestion that we occupy a privileged position near the center of a large, nonlinear, and nearly spherical void has recently attracted much attention as an alternative to dark energy." [3] Looking not only at supernova data but also at the cosmic microwave background spectrum, Big Bang nucleosynthesis and other factors, they concluded that "voids are in severe tension with the data. In particular, void models predict a very low local Hubble rate, suffer from an "old age problem", and predict much less local structure than is observed." [3]

Local void models propose a large area of lower than average density, so they ordinarily make or imply stochastic predictions that can be falsified by astronomical surveys. For example, under a local void model, an unusually low number of nearby galaxies would be expected, so observations indicating an average number of nearby galaxies would constitute disconfirming evidence. Data from an infrared survey released in 2003, the Two Micron All Sky Survey, is suggested to accord with a local underdensity of approximately 200 megaparsecs (Mpc) in diameter. [8] This hypothesis has received additional support from further studies of photometric and spectroscopic galaxy surveys. [9] [10] Furthermore, larger voids (KBC Void) out to 600 Mpc scale have been proposed on the basis of studies of galaxy luminosity density. [11]

Relationship to Hubble Tension

Measurements of the Hubble constant vary, with recent figures typically ranging from approximately 64 to 82 (km/s)/Mpc — a difference considered too significant to be explained by chance and too persistent to be explained by error. [12] Measurements of the cosmic microwave background tend to result in lower values than measurements by other means, such as photometry and cosmic distance ladder. For example, cosmic background radiation data from the Atacama Cosmology Telescope implies that the universe should be expanding more slowly than is locally observed. [13] In 2013, luminosity density measurements were made of galaxies from a broad sample of spectroscopic surveys. The resulting statistical analysis implies that the local mass density may be lower than the universe's average mass density. The scale and amplitude of this underdensity could resolve the apparent discrepancy between direct local measurements of the Hubble constant and values calculated from Planck's measurements of the cosmic microwave background. [11]

See also

Related Research Articles

<span class="mw-page-title-main">Copernican principle</span> Principle that humans are not privileged observers of the universe

In physical cosmology, the Copernican principle states that humans are not privileged observers of the universe, that observations from the Earth are representative of observations from the average position in the universe. Named for Copernican heliocentrism, it is a working assumption that arises from a modified cosmological extension of Copernicus' argument of a moving Earth.

<span class="mw-page-title-main">Accelerating expansion of the universe</span> Cosmological phenomenon

Observations show that the expansion of the universe is accelerating, such that the velocity at which a distant galaxy recedes from the observer is continuously increasing with time. The accelerated expansion of the universe was discovered in 1998 by two independent projects, the Supernova Cosmology Project and the High-Z Supernova Search Team, which used distant type Ia supernovae to measure the acceleration. The idea was that as type Ia supernovae have almost the same intrinsic brightness, and since objects that are further away appear dimmer, the observed brightness of these supernovae can be used to measure the distance to them. The distance can then be compared to the supernovae's cosmological redshift, which measures how much the universe has expanded since the supernova occurred; the Hubble law established that the further away an object is, the faster it is receding. The unexpected result was that objects in the universe are moving away from one another at an accelerating rate. Cosmologists at the time expected that recession velocity would always be decelerating, due to the gravitational attraction of the matter in the universe. Three members of these two groups have subsequently been awarded Nobel Prizes for their discovery. Confirmatory evidence has been found in baryon acoustic oscillations, and in analyses of the clustering of galaxies.

<span class="mw-page-title-main">Hubble's law</span> Observation in physical cosmology

Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving away. For this purpose, the recessional velocity of a galaxy is typically determined by measuring redshift, a shift in the light it emits toward the red end of the visible light spectrum. The discovery of Hubble's law is attributed to work published by Edwin Hubble in 1929.

<span class="mw-page-title-main">Reionization</span> Process that caused matter to reionize early in the history of the Universe

In the fields of Big Bang theory and cosmology, reionization is the process that caused electrically neutral atoms in the universe to reionize after the lapse of the "dark ages".

<span class="mw-page-title-main">Age of the universe</span> Time elapsed since the Big Bang

In physical cosmology, the age of the universe is the time elapsed since the Big Bang. Astronomers have derived two different measurements of the age of the universe: a measurement based on direct observations of an early state of the universe, which indicate an age of 13.787±0.020 billion years as interpreted with the Lambda-CDM concordance model as of 2021; and a measurement based on the observations of the local, modern universe, which suggest a younger age. The uncertainty of the first kind of measurement has been narrowed down to 20 million years, based on a number of studies that all show similar figures for the age. These studies include researches of the microwave background radiation by the Planck spacecraft, the Wilkinson Microwave Anisotropy Probe and other space probes. Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang, and measurements of the expansion rate of the universe can be used to calculate its approximate age by extrapolating backwards in time. The range of the estimate is also within the range of the estimate for the oldest observed star in the universe.

<span class="mw-page-title-main">Lambda-CDM model</span> An anomaly in astronomical observations of the Cosmic Microwave Background

The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components:

  1. a cosmological constant, denoted by lambda (Λ), associated with dark energy
  2. the postulated cold dark matter, denoted by CDM
  3. ordinary matter
<span class="mw-page-title-main">Expansion of the universe</span> Increase in distance between parts of the universe over time

The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion, so it does not mean that the universe expands "into" anything or that space exists "outside" it. To any observer in the universe, it appears that all but the nearest galaxies recede at speeds that are proportional to their distance from the observer, on average. While objects cannot move faster than light, this limitation applies only with respect to local reference frames and does not limit the recession rates of cosmologically distant objects.

<span class="mw-page-title-main">Pavo–Indus Supercluster</span> Neighboring supercluster in the constellations Pavo, Indus and Telescopium

The Pavo–Indus Supercluster is a neighboring supercluster located about 60–70 Mpc (196–228 Mly) away in the constellations of Pavo, Indus, and Telescopium. The supercluster contains three main clusters, Abell 3656, Abell 3698, and Abell 3742.

<span class="mw-page-title-main">Dark energy</span> Energy driving the accelerated expansion of the universe

In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. Assuming that the lambda-CDM model of cosmology is correct, dark energy dominates the universe, contributing 68% of the total energy in the present-day observable universe while dark matter and ordinary (baryonic) matter contribute 26% and 5%, respectively, and other components such as neutrinos and photons are nearly negligible. Dark energy's density is very low: 7×10−30 g/cm3, much less than the density of ordinary matter or dark matter within galaxies. However, it dominates the universe's mass–energy content because it is uniform across space.

<span class="mw-page-title-main">Local Void</span> Vast void adjacent to the Local Group

The Local Void is a vast, empty region of space, lying adjacent to the Local Group. Discovered by Brent Tully and Rick Fisher in 1987, the Local Void is now known to be composed of three separate sectors, separated by bridges of "wispy filaments". The precise extent of the void is unknown, but it is at least 45 Mpc across, and possibly 150 to 300 Mpc. The Local Void appears to have significantly fewer galaxies than expected from standard cosmology.

<span class="mw-page-title-main">Baryon acoustic oscillations</span> Fluctuations in the density of the normal matter of the universe

In cosmology, baryon acoustic oscillations (BAO) are fluctuations in the density of the visible baryonic matter of the universe, caused by acoustic density waves in the primordial plasma of the early universe. In the same way that supernovae provide a "standard candle" for astronomical observations, BAO matter clustering provides a "standard ruler" for length scale in cosmology. The length of this standard ruler is given by the maximum distance the acoustic waves could travel in the primordial plasma before the plasma cooled to the point where it became neutral atoms, which stopped the expansion of the plasma density waves, "freezing" them into place. The length of this standard ruler can be measured by looking at the large scale structure of matter using astronomical surveys. BAO measurements help cosmologists understand more about the nature of dark energy by constraining cosmological parameters.

<span class="mw-page-title-main">NGC 5584</span> Galaxy in the constellation Virgo

NGC 5584 is a barred spiral galaxy in the constellation Virgo. It was discovered July 27, 1881 by American astronomer E. E. Barnard. Distance determination using Cepheid variable measurements gives an estimate of 75 million light years, whereas the tip of the red-giant branch approach yields a distance of 73.4 million light years. It is receding with a heliocentric radial velocity of 1,637 km/s. It is a member of the Virgo III Groups, a series of galaxies and galaxy clusters strung out to the east of the Virgo Supercluster of galaxies.

The cosmic age problem was a historical problem in astronomy concerning the age of the universe. The problem was that at various times in the 20th century, the universe was estimated to be younger than the oldest observed stars. Estimates of the universe's age came from measurements of the current expansion rate of the universe, the Hubble constant , as well as cosmological models relating to the universe's matter and energy contents. Issues with measuring as well as not knowing about the existence of dark energy led to spurious estimates of the age. Additionally, objects such as galaxies, stars, and planets could not have existed in the extreme temperatures and densities shortly after the Big Bang.

<span class="mw-page-title-main">Void (astronomy)</span> Vast empty spaces between filaments with few or no galaxies

Cosmic voids are vast spaces between filaments, which contain very few or no galaxies. In spite of their size, most galaxies are not located in voids. This is because most galaxies are gravitationally bound together, creating huge cosmic structures known as galaxy filaments. The cosmological evolution of the void regions differs drastically from the evolution of the universe as a whole: there is a long stage when the curvature term dominates, which prevents the formation of galaxy clusters and massive galaxies. Hence, although even the emptiest regions of voids contain more than ~15% of the average matter density of the universe, the voids look almost empty to an observer.

Idit Zehavi is an Israeli astrophysicist and researcher who discovered an anomaly in the mapping of the cosmos, which offered insight into how the universe is expanding. She is part of the team completing the Sloan Digital Sky Survey and is one of the world's most highly cited scientists according to the list published annually by Thomson Reuters.

<span class="mw-page-title-main">Dipole repeller</span> Center of effective repulsion in the large-scale flow of galaxies near the Milky Way

The dipole repeller is a center of effective repulsion in the large-scale flow of galaxies in the neighborhood of the Milky Way, first detected in 2017. It is thought to represent a large supervoid, the Dipole Repeller Void.

The KBC Void is an immense, comparatively empty region of space, named after astronomers Ryan Keenan, Amy Barger, and Lennox Cowie, who studied it in 2013. The existence of a local underdensity has been the subject of many pieces of literature and research articles.

Sangeeta Malhotra is an astrophysicist who studies galaxies, their contents, and their effects on the universe around them. The objects she studies range from our own Milky Way galaxy to some of the earliest and most distant known galaxies in the epoch of cosmic dawn.

References

  1. 1 2 3 "Hubble Bubble". The Astronomist. 29 July 2010. Retrieved 2 February 2011.
  2. 1 2 Conley, A; RG Carlberg; J Guy; DA Howell; S Jha; A Riess; M Sullivan (2007). "Is there evidence for a Hubble Bubble? The nature of Type Ia supernova colors and dust in external galaxies". Astrophysical Journal. 664 (1): L13–L16. arXiv: 0705.0367 . Bibcode:2007ApJ...664L..13C. doi:10.1086/520625. S2CID   11074723.
  3. 1 2 3 4 Moss, Adam; James P Zibin; Douglas Scott (2011). "Precision Cosmology Defeats Void Models for Acceleration". Physical Review D. 83 (10): 103515. arXiv: 1007.3725 . Bibcode:2011PhRvD..83j3515M. doi:10.1103/PhysRevD.83.103515. S2CID   119261120.
  4. ↑ Kenworthy, W. D'Arcy; Scolnic, Dan; Riess, Adam (2019-04-24). "The Local Perspective on the Hubble Tension: Local Structure Does Not Impact Measurement of the Hubble Constant". The Astrophysical Journal. 875 (2): 145. arXiv: 1901.08681 . Bibcode:2019ApJ...875..145K. doi: 10.3847/1538-4357/ab0ebf . ISSN   1538-4357. S2CID   119095484.
  5. ↑ Freedman, Wendy L. (2021-09-17). "Measurements of the Hubble Constant: Tensions in Perspective*". The Astrophysical Journal. 919 (1): 16. arXiv: 2106.15656 . Bibcode:2021ApJ...919...16F. doi: 10.3847/1538-4357/ac0e95 . ISSN   0004-637X. S2CID   235683396.
  6. 1 2 Zehavi, Idit; Adam G Riess; Robert P Kirshner; Avishai Dekel (1998). "A Local Hubble Bubble from Type IA Supernovae?". Astrophysical Journal. 503 (2): 483. arXiv: astro-ph/9802252 . Bibcode:1998ApJ...503..483Z. doi:10.1086/306015. S2CID   122223606.
  7. ↑ Overbye, Dennis (February 22, 2010). "From the Clash of White Dwarfs, the Birth of a Supernova". New York Times. Retrieved 6 February 2011.
  8. ↑ Frith, W. J.; Busswell, G. S.; Fong, R.; Metcalfe, N.; Shanks, T. (November 2003). "The local hole in the galaxy distribution: evidence from 2MASS". Monthly Notices of the Royal Astronomical Society. 345 (3): 1049–1056. arXiv: astro-ph/0302331 . Bibcode:2003MNRAS.345.1049F. doi: 10.1046/j.1365-8711.2003.07027.x . S2CID   2115068.
  9. ↑ Busswell, G. S.; Shanks, T.; W. J. Frith, P. J. O.; Metcalfe, N.; Fong, R. (2004-11-11). "The local hole in the galaxy distribution: new optical evidence". Monthly Notices of the Royal Astronomical Society. 354 (4): 991–1004. arXiv: astro-ph/0302330 . Bibcode:2004MNRAS.354..991B. doi: 10.1111/j.1365-2966.2004.08217.x . ISSN   0035-8711. S2CID   18260737.
  10. ↑ Whitbourn, J. R.; Shanks, T. (2014-01-21). "The Local Hole revealed by galaxy counts and redshifts". Monthly Notices of the Royal Astronomical Society. 437 (3): 2146–2162. arXiv: 1307.4405 . doi: 10.1093/mnras/stt2024 . ISSN   0035-8711.
  11. 1 2 Keenan, Ryan C.; Barger, Amy J.; Cowie, Lennox L. (2013). "Evidence for a ~300 Mpc Scale Under-density in the Local Galaxy Distribution". The Astrophysical Journal. 775 (1): 62. arXiv: 1304.2884 . Bibcode:2013ApJ...775...62K. doi:10.1088/0004-637X/775/1/62. S2CID   118433293.
  12. ↑ Riess, Adam G.; Casertano, Stefano; Yuan, Wenlong; Macri, Lucas M.; Scolnic, Dan (18 March 2019). "Large Magellanic Cloud Cepheid Standards Provide a 1% Foundation for the Determination of the Hubble Constant and Stronger Evidence for Physics Beyond LambdaCDM". The Astrophysical Journal. 876 (1): 85. arXiv: 1903.07603 . Bibcode:2019ApJ...876...85R. doi: 10.3847/1538-4357/ab1422 . S2CID   85528549.
  13. ↑ Castelvecchi, Davide (2020-07-15). "Mystery over Universe's expansion deepens with fresh data". Nature. 583 (7817): 500–501. Bibcode:2020Natur.583..500C. doi: 10.1038/d41586-020-02126-6 . PMID   32669728. S2CID   220583383.
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