Is dark matter real...?
... and the star transformed into a musical instrument
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Main story: Is dark matter real?
Look at the image of the Andromeda galaxy above. You’re staring at a vast stellar metropolis containing perhaps as many as a trillion stars. That’s enough for every single person on Earth to have over one hundred each.
Yet what is keeping such a gargantuan mass of stars together? You may think the answer is gravity, but it isn’t quite that straightforward. The stars on the edge of galaxies like Andromeda are moving so fast that they should fly off into space. There simply isn’t enough gravity to hold on to them.
And yet the stars remain silently swirling around the galaxy. Why don’t they escape?
There are two broad and radically different approaches to answering this question.
The first is that there is extra gravity we aren’t accounting for, provided by so-called dark matter strewn throughout the galaxy. If true, dark matter would also help keep our own Milky Way together and there would be so much of it that a particle of dark matter passes through your body every minute. And yet, despite numerous extensive and exhaustive searches, physicists have never found a single particle of dark matter.
Which leaves the door ajar to the other possibility: that the ‘missing’ gravity comes from the fact that we’ve misunderstood gravity itself. That gravity works differently on the scale of galaxies compared to the scale of the solar system. This is the arena of so-called Modified Newton Dynamics (MOND).
This week saw a new chapter added to the long running drama. Researchers from Sejong University, in Seoul, South Korea, believe they have found “smoking gun” evidence of the variability of gravity. They used data from the Gaia telescope to look at tens of thousands of wide binaries - two stars circling around one another separated by a large distance.
The Korean scientists found that the stars’ orbits deviate from predictions made using the gravitational equations made famous by Newton and Einstein. The stars’ accelerations seem to be 30 to 40 per cent higher. Apply the same logic to stars on the edges of galaxies and they would be able to move faster than Newton’s equations allow. There would be no need for ‘extra’ gravity or invisible dark matter at all.
It’s far from an open-and-shut case, but maybe - just maybe - astronomers have taken a big step closer to understanding one of the deepest mysteries in the universe.
FACT OF THE WEEK
It would take you 211 million years to walk a light year - you would need to have left Earth not long after the first dinosaurs appeared to be nearing the end of your journey now
AUDIO
How many bananas would it take to get to Mars?
ASTRONOMY FOR BEGINNERS ONLINE COURSE
10% DISCOUNT WITH CODE “SUBSCRIBER”
I’m running my Astronomy for Beginners course as a series of live online classes from 12 September - 17 October 2023. Discover the secrets behind eclipses, fly through the solar system and learn how to observe the night sky with your eyes, binoculars and a telescope. All classes are recorded, so if you can’t make all the sessions, or just prefer to watch in your own time, you won’t miss out.
What have I been up to?
I recently wrote an article for BBC Science Focus magazine on the possibility of aliens using a supernova explosion as a beacon to send us a message
In other news…
NASA re-establishes full contact with Voyager 2 after a glitch
Entire star transformed into a musical instrument
Two stars orbiting each other so closely that they could fit inside the Sun
