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Both push and pull drive our Galaxy’s race through space

30-01-2017

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 flow 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.

 

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22-05-2017

Hebrew University search committee recommends Rector Asher Cohen for President

Following a rigorous search process, a presidential search committee has unanimously recommended that the universitys Rector, Prof. Asher Cohen, be elected President

17-05-2017

2017 Annual Lionel Cohen Lecture

The guest speaker was the Right Honourable the Lord Thomas of Cymgiedd Lord Chief Justice of England and Wales

15-05-2017

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08-05-2017

The New CyberLaw Programme

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02-05-2017

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To Members of the International Board of Governors of The Hebrew University of Jerusalem

We join our American Friends in mourning the passing of our dear friend Harvey M. Krueger.

26-04-2017

Statement from the Hebrew University of Jerusalem

The Hebrew University and the Rothberg International School express our deep sorrow over the murder of Hannah Bladon

15-04-2017

Hebrew University Launches Multidisciplinary Centre on Cannabinoid Research

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05-04-2017

20th annual Sternberg Ceremony at the Hebrew University

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04-04-2017

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04-04-2017

Teacher-Scholars Programme at the Faculty of Science of the Hebrew University of Jerusalem

Without these teachers, many of these high schools simply wouldn't have science teachers

30-03-2017

High burden of Iodine deficiency found in Israel’s first national survey

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27-03-2017

The 64th Annual Dinner of the Legal Group of the British Friends of the Hebrew University

The evening was hosted by Lord Pannick QC, Chairman of the Legal Group

16-03-2017

Intel Buying Mobileye For $15 Billion In Biggest Israel Hi-Tech Deal Ever

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13-03-2017

Home Instruction for Parents and Preschool Youngsters (HIPPY) Programme to be Launched in Korea

Yissum Research Development Company of the Hebrew University, announced today that it has signed an agreement with Lolo Educational Services Co., Korea

08-03-2017

Hebrew University is the First Israeli Academic Institute to Recognize Palestinian Test Results

This new policy will significantly increase the number of East Jerusalem Palestinians who attend the University

02-03-2017

Germany’s Order of Merit Awarded to Hebrew University President Menahem Ben-Sasson

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01-03-2017

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27-02-2017

‘Smart’ bacteria remodel their genes to infect our intestines

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22-02-2017

Israeli and Palestinian Researchers Cooperate to Find Risk Factors for B Cell Non-Hodgkin Lymphoma

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19-02-2017

Focus on Lord Pannick, QC, Chairman of BFHU Legal Group

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09-02-2017

Bacteria Sleep, Then Rapidly Evolve, to Survive Antibiotic Treatments

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06-02-2017

Science Brings Tomatoes Back Their Good Old Flavour

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05-02-2017

Israel Prize to be Awarded to Hebrew University Prof. Yehuda Liebes

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05-02-2017

Both push and pull drive our Galaxy’s race through space

Discovery of the Dipole Repeller confirms that both attraction and repulsion are at play in our extragalactic neighbourhood

30-01-2017

Dyslexia Linked to Shorter Memory Trace of Previous Stimuli

Hebrew University Researchers provide new insight into the brain mechanisms underlying a condition that causes reading and writing difficulties

25-01-2017

More Dead Sea Scrolls Fragments Found in the Cave of Skulls

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

US and Israeli researchers join forces by applying nanotechnology to cancer research

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10-01-2017

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10-01-2017

Of Mice and Men: Unique Electrical Properties of Human Nerve Cells Make a Difference

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Addressing War, Crime and Privacy in Cyberspace

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