On July 1, a Falcon 9 rocket will blast off from a Florida launch pad carrying the Euclid space telescope, a three-mirror Korsch-type telescope for peering at extremely distant galaxies.
The ESA won’t be looking for a lump of dark matter or something like that, but rather for evidence of other, regular matter interacting with the gravitational pull that dark matter generates. One of the places they expect to find it is the objects behind large galaxies, whose light is bent around them by the galaxy’s powerful gravity, allowing us to see them here on Earth.
The phenomenon is called gravitational lensing and its observation was taken as proof that Albert Einstein’s theory of general relativity is accurate.
That light gets bent and warped into curved shapes as part of this lensing process, and by measuring just how that happens, scientists using the Euclid telescope will hopefully be able to understand more about how dark matter works.
Mysterious Forces
The name “dark matter” is something of a misnomer, as is the similarly-named “dark energy.” Both are stand-ins for phenomena of which the effects of their existence have been observed - effects that have no obvious cause.
In particular dark energy is the mystery force used to explain why the universe keeps accelerating outward from the ultra-condensed form it had at the time of the Big Bang. According to the amount of energy that can be observed, that shouldn’t be happening, leading scientists to conclude that some enormous amount of unseen matter must exist that’s causing it to do so.
According to their estimates, dark matter and dark energy make up as much as 95% of the energy density of the universe.
Because of its elusive properties, which have been known for close to a century, scientists have struggled to firmly pin down dark matter or dark energy.
Teaming Up
The Euclid mission will build on others, including another by the ESA that operated from 2009 to 2013, called the Planck satellite.
In 2027, Euclid will get a companion in this project in the form of the Nancy Grace Roman Space Telescope, which will be launched by the US space agency NASA.
“Twenty-five years after its discovery, the universe’s accelerated expansion remains one of the most pressing mysteries in astrophysics,” Jason Rhodes, the deputy project scientist for the Roman telescope, the US science lead for the Euclid program, and a senior research scientist at NASA’s Jet Propulsion Laboratory, said in a news release.
“With these upcoming telescopes, we will measure dark energy in different ways and with far more precision than previously achievable, opening up a new era of exploration into this mystery.”
The two satellites will complement each other in several ways.
Euclid will observe a far larger area of the sky than Roman: about 15,000 square degrees, or one-third of the sky, using both infrared and optical wavelengths of light, but with less detail than Roman. It will be able to observe galaxies 10 billion light-years away, dating to a time when the universe was a sprightly 3 billion years old.
Roman, on the other hand, will only look at about 2,000 square degrees of sky, or one-twentieth of the sky. However, it will be able to see a further billion light-years away than Euclid will, observing even fainter galaxies. Roman will also be able to perform multiple roles, including looking at closer objects, such as nearer galaxies or even planets in our own solar system.