An array of 48 telescopes built in the Arava is intended, among other things, to discover planets orbiting white dwarfs and to find out what remains of solar systems after the death of their star.
Almost every star similar to the Sun will end its life aswhite dwarf — A small, hot, dense core that remains after a star swells into a red giant and sheds its outer layers. But what happens to the planets that orbited it? Are they swallowed up or thrown out of the system, do some of them survive, and can new worlds settle into orbit around the remnant? An Israeli telescope array is designed to help answer these questions.
Dr. Sagi Ben-Ami, experimental astrophysicist from the Department of Particle Physics andAstrophysics At the Weizmann Institute of Science, partner in establishing the LAST survey telescope at the institute's LEED Observatory Neot Smadar in the Arava. The system is made up of dozens of small telescopes working together, and in its full configuration it includes 48 telescopes. One of its scientific goals is to search for planets around white dwarfs.
The distant future of the solar system
A star like the Sun spends most of its life fusing hydrogen at its core. As its nuclear fuel runs out, the star swells into a red giant. At this point, nearby planets may be swallowed up, while the orbits of more distant worlds are altered as the star loses mass. At the end of the process, the dense core—the white dwarf—and parts of the original planetary system, if they survived the upheaval, are left behind.
A white dwarf contains a mass roughly comparable to that of the Sun within a body about the size of Earth. It is very hot at the beginning of its life, and then slowly cools over billions of years. Disks of dust, asteroid fragments, and heavy material that fell to the surface of the star have already been found around white dwarfs. These findings are evidence that planetary systems do not necessarily disappear when the star dies.
Can a planet survive?
For a planet to orbit a white dwarf in close orbit, it must undergo a complex evolutionary path. It may have formed with the star and survived at a safe distance, then migrated inward through gravitational interactions with other bodies. Another possibility is that material left over from the star's death recrystallized into small bodies. Researchers don't yet know how common each scenario is.
At least one giant planet orbiting a white dwarf, WD 1856 b, has already been discovered, but the big question is whether small rocky worlds also exist. Discovering a population of such planets would allow us to examine how solar systems change after the death of their central star, and provide a glimpse into the distant future of our solar system.
A big advantage for a small star
One of the main ways to detect extrasolar planets is The transition methodWhen a planet passes between us and its star, it blocks some of the light, causing a periodic dip in brightness. Around a normal sun-like star, an Earth-sized planet blocks only a tiny fraction of the light. By contrast, a white dwarf is similar in size to Earth, so a rocky planet passing in front of it can block a large portion of the light—sometimes even most of it.
This advantage comes with a difficulty: the white dwarf is small, and planets in close orbits move quickly. The transit can last only a few minutes. Not to miss it requires a survey that images large areas of the sky repeatedly, at a high rate. This is where the LAST array comes into play.
48 telescopes instead of one giant telescope
In its planned configuration, LAST includes forty-eight telescopes, each with a mirror diameter of about 28 centimeters. They are mounted in groups on 12 independent tripods and can be operated flexibly: several telescopes can be directed to the same field to deepen the observation, or they can be directed to different areas to quickly scan an extremely large area.
The array's total field of view may reach about 355 square degrees, and the light-gathering area of the 48 telescopes together is approximately equivalent to that of a single 1.9-meter telescope. The combination of a wide field, high-frequency imaging, and relatively low cost makes it possible to search for short, elusive phenomena—including transits of planets in front of white dwarfs.
The array is not designed for this mission alone. It can track supernovae and other transient events, search for near-Earth objects, and scan large areas where a flash of light may appear following a gravitational wave event. The modular structure allows for several observing programs to be carried out simultaneously.
The ability to search for signs of life
A sufficiently cooled white dwarf may have a region around it where the temperature is such that liquid water can exist on the surface of a planet. This region is very close to the star, so the planet's orbital period may be short. Frequent transits make it easy to accumulate many observations and verify that the dimming is indeed cyclical.
If a suitable rocky planet is found, it would be possible to try to analyze the light passing through its atmosphere during the transit. Because the white dwarf is small, the ratio of the planet's atmospheric area to the star's area may be easier to measure than in a Sun-Earth system. However, Yeshiv area Not proof of life: It must be checked whether the planet has retained an atmosphere and water and whether the radiation environment allows for stable conditions over time.
LAST's observations are primarily designed to find the rare systems and identify promising candidates. Larger telescopes, on the ground and in space, can then make follow-up observations to determine the planet's size, orbit, and whether anything can be learned about its atmosphere.
The research and establishment of the system were supported, among other things, by the Israel Science Foundation.
Questions and Answers
What is a white dwarf?
A white dwarf is the dense core left over from a low- to medium-mass star after it has completed its primary fusion stages and shed its outer layers. It is about the size of Earth, but its mass can be similar to that of the Sun.
How can you discover a planet around a white dwarf?
One method is to measure a brief, periodic dip in the dwarf's brightness when a planet passes in front of it. Because a white dwarf is small, even a rocky planet could block a significant portion of its light.
Why are dozens of small telescopes needed?
A modular array allows for imaging large fields of sky at high frequency, or combining several telescopes for deeper observations. This increases the chance of capturing short events, including transits lasting only minutes.
Can life exist around a white dwarf?
Theoretically, a zone around a white dwarf could exist where the temperature is suitable for liquid water. However, many additional conditions are required, including a stable atmosphere and a history that allowed the planet to survive or reach its orbit after the red giant phase.
The scientific article
More on the subject on the science website
- The survey telescope with the largest field of view in the world was inaugurated in the Arava.
- Astronomers have recorded a mysterious shock wave around a white dwarf
- Planet-devouring star observed for the first time
- Hotter than the Sun: An extremely hot brown dwarf discovered alongside a white dwarf
For the original publication: [Around the White Dwarf — Voice of Science website, National Science Foundation](
