STARGAZING: Dark matter, what is it?

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton

The Earth, other planets, and all the stars and galaxies we can see add up to about 16 per cent of the material making up the universe.

The other 84 per cent is invisible. However, it’s there, or something is, because we see its gravitational influence almost everywhere. If we measure the orbit of the Moon, we can calculate its mass. When we measure the orbits of stars around their galaxies, and do the same calculation, we end up with several times more mass than we can see. Someone started referring to this invisible stuff as “Dark Matter”, and the name stuck. However, nobody is happy with the idea of a mystery ingredient that makes our calculations work but is otherwise undetectable, so the quest is on to find out what Dark Matter is. One possibility is that our ideas about gravity are not correct, but could they be incorrect to the extent of 84% of the mass of the universe?

So far our knowledge about gravity has worked very well. Even though we still don’t know exactly what it is, we can use it to navigate our spacecraft around the Solar System and model the collapse of clouds to form stars and planetary systems. We have also used it in searching for new planets, by measuring their gravitational tugging at known bodies. We are fairly reluctant to accept – yet – that something is grossly wrong with our gravitational calculations. What else is there?

One possibility is an unknown particle, that is heavy enough to create strong gravitational effects, but otherwise does not react much with anything else. These have become known as WIMPS (weakly interacting massive particles). This might sound like the fudge factor we started with – an undetectable something that makes our calculations work. However, according to our understanding of how elementary particles work, WIMPS, if they exist, should be detectable. If 84% of the universe is made up of WIMPS, there are lots of them around. Even if they only interact with our kind of matter occasionally, there should still be enough interactions for us to detect some. That is the objective of the LUX experiment. Lux is Latin for light, and is also the acronym for the Large Underground Xenon experiment. Deep in a mine in South Dakota there is a large tank containing 350 kg of liquid xenon. The tank is lightproof, and inside the tank are many sensitive light detectors. The device is deep in a mine to use the Earth to screen out any cosmic rays and “strongly interacting particles” from space.  WIMPS would easily penetrate down to the detector, and possibly collide with one of the xenon atoms, producing a flash of light, which will be detected.  Xenon atoms are particularly big targets. The project has been running now for about three years and as yet has detected no WIMPS. These particles are either even more wimpy than predicted, or they don’t exist at all.

However, the idea that Dark Matter is made up of some sort of particle is still the most popular among scientists, so there are plans to make an even bigger detector, containing 7 tonnes of xenon. Experience so far suggests that patience will be an important component in this search. How long will it take to produce a credible negative result? Since the idea that Dark Matter is made up of particles is largely in agreement with our current understanding of particle physics, this is the most widely accepted idea. If these detectors don’t find any WIMPS or other Dark Matter particles, how long will it take to establish a solid negative result? If no WIMPS turn up, our ideas about the nature of space and the dynamics of the universe could be in for another upset. Is there something wrong with our understanding of gravity? Stay tuned!

Venus lies very low in the after-sunset glow, but might be visible as a bright, starlike object. Mars and Saturn lie very low in the southwest after dark. Mars is on the left and Saturn on the right. The Moon will be New on the 30th.

Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astrophysical Observatory, Penticton

Just Posted

Princess Maggie presents Children’s Winter Carnival on Dec. 14

The Leadership class is hosting the event from 12:30 to 4 p.m.

Police plan forum in Hedley to address resident concerns

Princeton RCMP will hold a meeting in Hedley this month, to address… Continue reading

Interior Health finds Penticton’s fatal overdose rate ‘alarming’

The rate has been consistenly increasing since 2015

Traffic into Penticton Public Library slows, attributed to safety concerns

Foot traffic into the Penticton Public Library is down four per cent,… Continue reading

Star Gazing: Binoculars on the Christmas list

Advice on buying a gift for the astronomer on your list

Sneak Peek: Army of Sass – Penticton present Joie de Vivre

Catch the winter showcase at the Cannery Stage on Dec. 7 with three showtimes

Funds approved for Keremeos Fire Department

$12,000 authorized for purchase of an intrusion and access control system

Residents in B.C. city could face 133% tax hike in ‘worst case’ lawsuit outcome: report

An average home could see a tax increase of $2,164 in one year

Bird populations significantly declining around Revelstoke says Parks Canada

Out of the mountain national parks, bird populations near Revelstoke are in the worst shape

Letter: Climate activists need to reconsider their advocacy efforts

“Deliberately denying these rights seems an inappropriate way to promote a cause.”

WATCH: Diehard Vernon Winter Carnival goers line up for tickets

Susan O’Brien was the first in line at 6:45 a.m. Friday

Letter: Save our Medicare

“Opposition to Dr. Day’s attempt to dismantle our medical system in Canada”

Letter: ‘Naughty’ Santa needs to do some reflecting

“The actions represent sexism and violence towards women.”

Letter: Time to end fossil fuel subsidies

“The clean economy is bringing in revenue for the government.”

Most Read