Both push and pull drive our Galaxy’s race through space30-01-2017
Discovery of the “Dipole Repeller” confirms that both attraction and repulsion are at play in our extragalactic neighbourhood
Although we can’t feel it, we’re in constant motion: the earth spins on its axis at about 1,600 km/h; it orbits around the sun at about 100,000 km/h; the sun orbits our Milky Way galaxy at about 850,000 km/h; and the Milky Way galaxy and its companion galaxy Andromeda are moving with respect to the expanding universe at roughly 2 million km/h (630 km per second). But what is propelling the Milky Way’s race through space?
Until now, scientists assumed that a dense region of the universe is pulling us toward it, in the same way that gravity made Newton’s apple fall to earth. The initial “prime suspect” was called the Great Attractor, a region of a half dozen rich clusters of galaxies 150 million light-years from the Milky Way. Soon after, attention was drawn to an area of more than two dozen rich clusters, called the Shapley Concentration, which sits 600 million light-years beyond the Great Attractor.
Now researchers led by Prof. Yehuda Hoffman at the Hebrew University of Jerusalem report that our galaxy is not only being pulled, but also pushed. In a new study in the forthcoming issue of Nature Astronomy, they describe a previously unknown, very large region in our extragalactic neighbourhood. Largely devoid of galaxies, this void exerts a repelling force on our Local Group of galaxies.
“By 3-d mapping the flow of galaxies through space, we found that our Milky Way galaxy is speeding away from a large, previously unidentified region of low density. Because it repels rather than attracts, we call this region the Dipole Repeller,” said Prof. Yehuda Hoffman. “In addition to being pulled towards the known Shapley Concentration, we are also being pushed away from the newly discovered Dipole Repeller. Thus it has become apparent that push and pull are of comparable importance at our location.”
The presence of such a low density region has been suggested previously, but confirming the absence of galaxies by observation has proved challenging. But in this new study, Hoffman, at the Hebrew university’s Racah Institutes of Physics, working with colleagues in the USA and France, tried a different approach.
Using powerful telescopes, among them the Hubble Space Telescope, they constructed a 3-dimensional map of the galaxy flow field. Flows are direct responses to the distribution of matter, away from regions that are relatively empty and toward regions of mass concentration; the large scale structure of the universe is encoded in the ï¬‚ow ï¬eld of galaxies. They studied the peculiar velocities – those in excess of the Universe’s rate of expansion – of galaxies around the Milky Way, combining different datasets of peculiar velocities with a rigorous statistical analysis of their properties. They thereby inferred the underlying mass distribution that consists of dark matter and luminous galaxies — over-dense regions that attract and under-dense ones that repel.
By identifying the Dipole Repeller, the researchers were able to reconcile both the direction of the Milky Way’s motion and its magnitude. They expect that future ultra-sensitive surveys at optical, near-infrared and radio wavelengths will directly identify the few galaxies expected to lie in this void, and directly confirm the void associated with the Dipole Repeller.
PHOTOS and VIDEO are available at http://irfu.cea.fr/dipolerepeller. Use of these materials is permitted on condition of respecting the publication embargo and including the proper credit information.
The evening was hosted by Lord Pannick QC, Chairman of the Legal Group16-03-2017
Yissum Research Development Company of the Hebrew University, announced today that it has signed an agreement with Lolo Educational Services Co., Korea08-03-2017
This new policy will significantly increase the number of East Jerusalem Palestinians who attend the University02-03-2017
The Order of Merit recognizes Prof. Ben-Sasson's outstanding, extensive, and personal commitment to German-Israeli relations in the field of science, and thus to the cooperation between our two nations01-03-2017
Study suggests that people 'live up to their name' with their facial appearance27-02-2017
Hebrew University researchers describe how infectious bacteria sense they are attached to intestinal cells and remodel their gene expression to exploit our cells and colonize our gut22-02-2017
In both groups, recreational sun exposure, black hair-dye use, a history of hospitalization for infection, and having a first-degree relative with a blood cancer were associated with B-NHL. Each group had unique risk factors too.19-02-2017
Lord Pannick, QC, at Blackstone Chambers, acted for the lead claimant Gina Miller in the historic 11-justice Supreme Court case.09-02-2017
Hebrew University biophysicists used quantitative approaches from Physics to understand issues in Biology09-02-2017
Hebrew University Truman Institute together with Scholas Occurrentes Educational Organization established by Pope Francis, are developing a conference and a programme on Culture of Encounter through Education in Jerusalem08-02-2017
Results obtained in a joint trial with Israel Electric Corporation (IEC)06-02-2017
Hebrew University researchers are part of an international team that identified the chemical compounds and the functional genes that give a tomato its great taste05-02-2017
Prof. Liebes, from the Department of Jewish Thought, awarded for his work in Kaballah and Jewish myth05-02-2017
Discovery of the Dipole Repeller confirms that both attraction and repulsion are at play in our extragalactic neighbourhood30-01-2017
Hebrew University Researchers provide new insight into the brain mechanisms underlying a condition that causes reading and writing difficulties25-01-2017
New fragments of the Dead Sea Scrolls have been uncovered by Archaeologists working on a salvage excavation in the Cave of Skulls by the Dead Sea in Israel.10-01-2017
American and Israeli research teams are preparing to explore treatments for cancer using science and engineering at the molecular level, commonly known as nanotechnology.10-01-2017
Bacteriophages (phages) are probably the most abundant entities in nature, often exceeding bacterial densities by an order of magnitude.10-01-2017
Scientists present first direct evidence that human neocortical neurons have unique membrane properties that enhance signal processing04-01-2017
States can no longer legislate solely within their own boundaries; project aims address war, crime and privacy in cyberspace04-01-2017