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MOND can explain dark matter ‘clincher’
This week–
Dimmer outlook for dark matter MARCUS CHOWN
THOUGH we can’t see it, dark matter is supposed to make up 22 per cent of the universe. Now it turns out it might not exist at all. Earlier this year, the discovery of a ring-like astronomical feature, invisible except for the way its gravity distorts background galaxies, was hailed as proof for the existence of dark matter and the death knell for a rival theory known as modified Newtonian dynamics (MOND). Not so, claims the father of MOND. “MOND perfectly explains the ring,” says Mordehai Milgrom
WHAT KIND OF PROPERTY DOES £175K BUY ON YOUR LATITUDE?
of the Weizmann Institute of Science in Rehovot, Israel. “In fact, it explains it more naturally than dark matter.” The ring-like feature is in a galaxy cluster called CL0024+17. It showed up when a team led by Myungkook James Jee, now at the University of California, Davis, observed the distortion of background galaxies by the cluster’s gravity. This revealed an ill-defined ring with a radius of about 1.2 million light years. Jee’s team interpreted it as a ring of invisible dark matter. According to Jee and his colleagues, CL0024+17 is in fact two
Garage, Chelsea, London
clusters, one hidden behind the other, and the ring of dark matter was created when the clusters collided sometime in the past. Think of the dark matter ring as like a smoke ring that formed at the collision point and grew outwards. Our view today is just a snapshot of this still-expanding ring. This doesn’t convince Milgrom and his colleague Bob Sanders of the Kapteyn Institute at the University of Groningen in the Netherlands. They now say that MOND provides a simpler explanation of the ring, which does not require any collision. “It’s a natural feature of MONDian gravity,” Milgrom says. In MOND, gravity changes from a form which weakens in the way Newton predicted to a stronger form that weakens more slowly. “In the transition region, gravity will shift to being stronger than Newtonian,” says Milgrom.
“Stronger gravity will bend the light of background galaxies more markedly, which is exactly the effect that led to the discovery of the ring.” Jee’s team dismissed the MOND explanation because they thought it predicts that there should be no enhanced gravity without visible matter to do the enhancing. “This
“MOND explains things naturally whereas dark matter proponents have to propose the existence of cold molecular gas” is a common misconception,” says Milgrom. “In fact, in MOND there does not necessarily have to be visible matter there to boost gravity – it is naturally boosted in the transition region.” No one knows what physics may underpin such a transition. “I am interested to hear that the
2 bedroom apartment, Cote d’Azur, France
Issued by HSBC Bank plc. HSBC Premier is subject to status and account opening criteria and local regulatory requirements. Featured information from independent sources. Figures correct at time of
NASA, ESA, STSCI/AURA
transition between the Newtonian and MONDian regime also gives rise to a ring,” says Jee. “In general, I am happy whenever there comes a theory which is simpler but can explain more observations.” According to Milgrom, MOND predicts the rough location of the ring in CL0024+17, which dark matter does not. It also predicts that such rings will be observed in other galaxy clusters and in spiral galaxies (www.arxiv.org/ abs/0709.2561). The crucial requirement is that a cluster be compact enough for the transition to MOND to occur outside where most of the cluster mass is concentrated, so its effect is clearly visible. This is the case in CL0024+17. “If such rings are found in all compact clusters it will strengthen the case for MOND, since the dark matter explanation requires –What holds it together?– collisions, which are relatively
rare,” Milgrom says. Milgrom and Sanders claim that the MOND transition will also be visible in compact single galaxies known as “high surface brightness galaxies”. They say there is tentative evidence of the transition in two such galaxies: UGC 3456 and UGC 11670. Stronger evidence may be found in three dwarf galaxies which were formed in galactic collisions near the galaxy NGC 5291, discovered this year by a team led by Frederic Bournaud of the French Atomic Energy Commission in Paris. “The collision should have stripped the galaxies of all their dark matter yet they still have enhanced gravity,” says Milgrom. “MOND explains things naturally whereas dark matter proponents have to propose the existence of yet another type of dark matter – cold molecular gas.” ●
Whilst your money undoubtedly goes a lot further in Thailand than in Chelsea, the process of buying a property abroad can be quite complex. With access to a global network, your Premier Relationship Manager will help you receive on-theground local knowledge to make your transaction run more smoothly. You can also talk directly to our local mortgage experts who will help you with the local regulations and arrange the right mortgage for you. Get more out of the world, visit www.hsbc.co.uk/premier or call 0800 432 0755. Your home may be repossessed if you do not keep up repayments on your mortgage. Beachside villa,Thailand
going to press. Lines are open 24 hours.Textphone 1800 10800 028 3516. Communications may be recorded and monitored for security and service improvement purposes.
AC7852
Dimmer outlook for dark matter MARCUS CHOWN
THOUGH we can’t see it, dark matter is supposed to make up 22 per cent of the universe. Now it turns out it might not exist at all. Earlier this year, the discovery of a ring-like astronomical feature, invisible except for the way its gravity distorts background galaxies, was hailed as proof for the existence of dark matter and the death knell for a rival theory known as modified Newtonian dynamics (MOND). Not so, claims the father of MOND. “MOND perfectly explains the ring,” says Mordehai Milgrom
WHAT KIND OF PROPERTY DOES £175K BUY ON YOUR LATITUDE?
of the Weizmann Institute of Science in Rehovot, Israel. “In fact, it explains it more naturally than dark matter.” The ring-like feature is in a galaxy cluster called CL0024+17. It showed up when a team led by Myungkook James Jee, now at the University of California, Davis, observed the distortion of background galaxies by the cluster’s gravity. This revealed an ill-defined ring with a radius of about 1.2 million light years. Jee’s team interpreted it as a ring of invisible dark matter. According to Jee and his colleagues, CL0024+17 is in fact two
Garage, Chelsea, London
clusters, one hidden behind the other, and the ring of dark matter was created when the clusters collided sometime in the past. Think of the dark matter ring as like a smoke ring that formed at the collision point and grew outwards. Our view today is just a snapshot of this still-expanding ring. This doesn’t convince Milgrom and his colleague Bob Sanders of the Kapteyn Institute at the University of Groningen in the Netherlands. They now say that MOND provides a simpler explanation of the ring, which does not require any collision. “It’s a natural feature of MONDian gravity,” Milgrom says. In MOND, gravity changes from a form which weakens in the way Newton predicted to a stronger form that weakens more slowly. “In the transition region, gravity will shift to being stronger than Newtonian,” says Milgrom.
“Stronger gravity will bend the light of background galaxies more markedly, which is exactly the effect that led to the discovery of the ring.” Jee’s team dismissed the MOND explanation because they thought it predicts that there should be no enhanced gravity without visible matter to do the enhancing. “This
“MOND explains things naturally whereas dark matter proponents have to propose the existence of cold molecular gas” is a common misconception,” says Milgrom. “In fact, in MOND there does not necessarily have to be visible matter there to boost gravity – it is naturally boosted in the transition region.” No one knows what physics may underpin such a transition. “I am interested to hear that the
2 bedroom apartment, Cote d’Azur, France
Issued by HSBC Bank plc. HSBC Premier is subject to status and account opening criteria and local regulatory requirements. Featured information from independent sources. Figures correct at time of
NASA, ESA, STSCI/AURA
transition between the Newtonian and MONDian regime also gives rise to a ring,” says Jee. “In general, I am happy whenever there comes a theory which is simpler but can explain more observations.” According to Milgrom, MOND predicts the rough location of the ring in CL0024+17, which dark matter does not. It also predicts that such rings will be observed in other galaxy clusters and in spiral galaxies (www.arxiv.org/ abs/0709.2561). The crucial requirement is that a cluster be compact enough for the transition to MOND to occur outside where most of the cluster mass is concentrated, so its effect is clearly visible. This is the case in CL0024+17. “If such rings are found in all compact clusters it will strengthen the case for MOND, since the dark matter explanation requires –What holds it together?– collisions, which are relatively
rare,” Milgrom says. Milgrom and Sanders claim that the MOND transition will also be visible in compact single galaxies known as “high surface brightness galaxies”. They say there is tentative evidence of the transition in two such galaxies: UGC 3456 and UGC 11670. Stronger evidence may be found in three dwarf galaxies which were formed in galactic collisions near the galaxy NGC 5291, discovered this year by a team led by Frederic Bournaud of the French Atomic Energy Commission in Paris. “The collision should have stripped the galaxies of all their dark matter yet they still have enhanced gravity,” says Milgrom. “MOND explains things naturally whereas dark matter proponents have to propose the existence of yet another type of dark matter – cold molecular gas.” ●
Whilst your money undoubtedly goes a lot further in Thailand than in Chelsea, the process of buying a property abroad can be quite complex. With access to a global network, your Premier Relationship Manager will help you receive on-theground local knowledge to make your transaction run more smoothly. You can also talk directly to our local mortgage experts who will help you with the local regulations and arrange the right mortgage for you. Get more out of the world, visit www.hsbc.co.uk/premier or call 0800 432 0755. Your home may be repossessed if you do not keep up repayments on your mortgage. Beachside villa,Thailand
going to press. Lines are open 24 hours.Textphone 1800 10800 028 3516. Communications may be recorded and monitored for security and service improvement purposes.
AC7852