Astronomers Are Creating Stars With Lasers, and the Reason Might Lead to New Worlds

There is one problem that ground-based telescopes face that astronomers can’t get around, no matter what they do. All light that is received has to go through the Earth’s atmosphere before it can reach the mirror of the telescope, and that atmosphere is full of air that is in motion, causing it to bend light that is received from other stars. This blurs the received image, making it hard for astronomers to view distant planets in other star systems. To combat this, astronomers have devised an innovative solution that is reminiscent of something out of science fiction. They have created their own stars in the sky by using lasers.

This has become one of the most powerful tools astronomers use to improve telescope performance and detect exoplanets that would otherwise go undetected.

Why Earth’s Atmosphere Blurs the Sky

Light from a distant star, entering Earth’s atmosphere, passes through layers of air that constantly shift in temperature and density. These variations bend the light slightly as it travels toward the ground. The effect is similar to looking at an object through moving water, where ripples distort the image.

Astronomers use a technology called adaptive optics to correct these distortions. According to research summarized by NASA’s Goddard Space Flight Center, adaptive optics systems rely on real-time measurements of atmospheric turbulence to enable telescope mirrors to adjust and compensate for the distortion.

However, adaptive optics requires a bright reference star near the target object. Without a reference point, the telescope cannot determine how the atmosphere is altering the incoming light.

Creating an Artificial Star

Also, astronomers developed laser guide stars to solve the shortage of natural reference stars. These artificial stars are created by projecting a powerful laser beam into the upper atmosphere.

The laser is tuned to a wavelength of about 589 nanometers, corresponding to the spectral signature of sodium atoms in a thin layer of the mesosphere, roughly 90 kilometers above Earth. When the laser reaches this region, it excites sodium atoms, causing them to glow and forming a bright point of light that acts like a star.

According to research from the Lawrence Livermore National Laboratory, the sodium layer naturally contains enough atoms to produce a visible artificial star when illuminated by the laser beam. The glowing spot remains fixed in the sky, providing a stable reference for adaptive optics systems to track.

Scientists at major observatories such as the W. M. Keck Observatory and Lick Observatory have demonstrated that these artificial stars enable telescopes to correct for atmospheric turbulence over much larger portions of the sky than would otherwise be possible.

How Adaptive Optics Corrects the Image

Once the artificial guide star appears in the sky, a telescope uses a wavefront sensor to analyze how the atmosphere distorts the light coming from that point. The sensor measures tiny changes in the shape of the incoming wavefront, which reveals how air turbulence has altered the path of the light.

A computer then calculates how a deformable mirror inside the telescope must deform to correct those distortions. The mirror contains hundreds of tiny actuators that adjust its surface thousands of times per second.

Studies published by SPIE describe how adaptive optics systems can operate at control-loop speeds approaching 1,000 corrections per second. This rapid response allows the telescope to flatten the distorted wavefront and produce a much sharper image.

The result is a dramatically smaller point spread function, which is the tiny region of light surrounding a star in a telescope image. A tighter point spread function means astronomers can distinguish faint planets located very close to their host stars.

A Powerful Tool for Finding Exoplanets

Laser guide stars have become particularly important for exoplanet research because they enable techniques that require extremely sharp images. One such method is direct imaging, in which astronomers block a star's bright light with a coronagraph and attempt to photograph the faint planet orbiting nearby.

Adaptive optics supported by laser guide stars improves the contrast between a star and its planet, making it easier to detect objects that would otherwise be lost in glare. According to studies published in the journal Monthly Notices of the Royal Astronomical Society, improved adaptive optics systems significantly enhance the ability to analyze exoplanet atmospheres using spectroscopic techniques.

These tools are expected to play a major role in future telescopes, including giant ground-based observatories designed to search for Earth-like planets.

Preparing for the Next Generation of Telescopes

The next generation of giant telescopes will rely even more on laser guide stars. The new Extremely Large Telescopes will use multiple lasers to create multiple artificial stars in the sky simultaneously.

A team of astronomers created a three-dimensional picture of the atmosphere's distortion of light from a star by measuring turbulence at multiple points. This enables the adaptive optics to correct the images over a wider field of view, offering the same level of clarity as a space-based telescope.

Those who have contributed to the development of adaptive optics have called the use of a laser guide star a revolutionary advance in astronomy. According to a team of scientists at Lawrence Livermore National Laboratory, using the sodium laser guide star creates an "artificial reference point in the sky," allowing the telescope to correct atmospheric turbulence and provide a much sharper view of the stars.

In practical terms, this means astronomers can explore much more of the sky while searching for faint worlds orbiting distant stars. What appears to be a simple beam of light aimed at the sky is actually one of the most powerful tricks modern astronomy has invented.