Astronomers get to ask some of the most fundamental questions of all, ranging from whether we are alone in the cosmos to what is the nature of the mysterious dark energy and dark matter that makes up most of the universe.
Now a large group of astronomers from all over the world are building the largest optical telescope ever in Chile: the Extremely Large Telescope (ELT). Once completed in 2028, construction could provide answers that transform our understanding of the universe.
With its 39 meter diameter primary mirror, the ELT will contain the largest, most perfect reflective surface ever built. Its light-gathering power will be greater than that of all other major telescopes combined, allowing it to detect objects millions of times fainter than the human eye can see.
There are several reasons why we need such a telescope. Its incredible sensitivity allows it to image some of the first galaxies ever formed, with light traveling 13 billion years to reach the telescope.
Observations of such distant objects could allow us to refine our understanding of cosmology and the nature of dark matter and dark energy.
Extraterrestrial life
The ELT may also provide an answer to the most fundamental question of all: are we alone in the universe?
The ELT is expected to be the first telescope to detect Earth-like exoplanets – planets that orbit other stars but have a similar mass, orbit and proximity to their host as Earth.
These Earth-like planets are in the so-called Goldilocks zone and orbit their star at just the right distance so that water cannot boil or freeze. This creates the conditions for the existence of life.
The ELT’s camera will have six times better resolution than that of the James Webb Space Telescope, allowing it to capture the clearest images of exoplanets yet. But as fascinating as these photos are, they don’t tell the whole story.
To find out whether life is likely to exist on an exoplanet, astronomers must supplement imaging with spectroscopy. While images reveal shape, size and structure, spectra tell us about the speed, temperature and even chemistry of astronomical objects.
The ELT will contain not one, but four spectrographs – instruments that disperse light into its component colors, much like the iconic prism on Pink Floyd’s The Dark Side of the Moon album cover.
These spectrographs are each about the size of a minivan and have been carefully checked for stability. They support all major scientific cases of the ELT.
For giant exoplanets, the Harmoni instrument will analyze the light that has traveled through their atmospheres, looking for signs of water, oxygen, methane, carbon dioxide and other gases that indicate the existence of life.
Detecting much smaller Earth-like exoplanets will require the more specialized Andes instrument. At a cost of around €35 million (£30 million), Andes will be able to detect small changes in the wavelength of light.
Previous satellite missions have given astronomers a good idea of where to look in the sky for exoplanets.
Indeed, several thousand confirmed or ‘candidate’ exoplanets have been discovered using the ‘transit method’. Here, a space telescope stares at a patch of sky with thousands of stars and looks for small, periodic dips in their intensity, caused when an orbiting planet passes in front of its star.
But Andes will use a different method to hunt other Earths. As an exoplanet orbits its parent star, gravity pulls on the star, causing it to wobble. This movement is incredibly small; Earth’s orbit causes the sun to oscillate at just 10 centimeters per second – the walking speed of a turtle.
Just as the pitch of an ambulance siren rises and falls as it moves toward and away from us, the wavelength of light seen from a wobbling star increases and decreases as the planet follows its orbit.
Remarkably, Andes will be able to detect this tiny change in the color of light. Although starlight is essentially continuous (“white”) from ultraviolet to infrared, it contains bands where atoms in the outer region of the star absorb specific wavelengths as the light escapes, making it appear dark in the spectra.
Small shifts in the positions of these features – about 1/10,000th of a pixel on the Andes sensor – can reveal the periodic fluctuations over months and years. This could ultimately help us find an Earth 2.0.
At Heriot-Watt University we are testing the development of a laser system known as a frequency comb, which will allow Andes to achieve such exquisite precision. Like the millimeter tapping on a ruler, the laser will calibrate the Andes spectrograph by delivering a spectrum of light structured as thousands of regularly spaced wavelengths.
This scale will remain constant for decades, limiting measurement errors that occur due to changes in temperature and pressure in the environment.
With the construction cost of the ELT reaching €1.45 billion, some may question the value of the project.
But astronomy has a meaning that spans millennia and transcends cultures and national boundaries. Only by looking far beyond our solar system can we gain a perspective that extends beyond the here and now.
Derryck Telford Reid, Professor of Physics, Heriot-Watt University
This article is republished from The conversation under a Creative Commons license. Read the original article.
