How can Proxima Centauri produce such powerful flares?
Proxima Centauri has only about 12% of the Sun’s mass and 14% of its radius. A small star, however, is not necessarily a quiet one. Inside Proxima, hot gas rises and cooler gas sinks through almost the entire star. This motion, together with the star’s rotation, generates a strong magnetic field. When energy stored in that field is suddenly released, a flare sends ultraviolet light, X-rays and radio emission surging.
Proxima lies about 4.24 light-years from the Sun and is our nearest star after the Sun itself. It is gravitationally bound to Alpha Centauri A and B, but unlike those two Sun-like stars, Proxima is a much smaller and dimmer red dwarf. Its total light indicates a surface temperature of about 2,900 K, or roughly 2,600°C. It emits more of its energy as invisible infrared light than as visible light.
- About 4.24 light-years Distance from the Sun to Proxima Centauri
- About 12% of the Sun Mass calculated from observations and stellar models
- About 14% of the Sun Radius calculated from observations and stellar models
- About 2,900 K Surface temperature, roughly 2,600°C
How is Proxima Centauri different from the Sun?
In the Sun, energy produced at the core moves outward in different ways through different internal layers. Models indicate that in a very low-mass star such as Proxima, convection—hot gas rising as cooler gas sinks—occurs through most of the interior. This circulation mixes hydrogen widely throughout the star. Proxima therefore ages differently from the Sun, which uses the hydrogen in its core first.
Lower mass means a cooler core and a slower rate of the nuclear fusion that turns hydrogen into energy. Proxima is far dimmer than the Sun, but it consumes its fuel so slowly that models predict it can continue hydrogen fusion for far longer. The universe is only about 13.8 billion years old, shorter than that predicted lifetime, so no one has yet observed the final stage of a red dwarf like this. It is known only from models of stellar evolution.
Proxima takes about 90 days to rotate once, compared with roughly 25 days for the Sun, yet it remains magnetically active. The hot gas inside the star contains electrically charged particles. Its movement and the star’s rotation work together to generate a magnetic field. Dark spots and bright regions on the surface also alter the star’s brightness and the colors in its light slightly as it turns.
How quickly does a flare brighten and fade?
Researchers observed Proxima simultaneously in ultraviolet, visible and radio wavelengths for about 40 hours in 2019. At the peak of the strongest flare in that period, its ultraviolet brightness briefly rose to about 14,000 times the usual level. This was the short-lived peak of one eruption, not the star’s average brightness.
Even during the same flare, different kinds of light brighten at different times and by different amounts. Ultraviolet light and X-rays reveal the hot gas in the star’s outer regions, while radio waves trace fast-moving electrons and the state of the magnetic field. Observing several wavelengths at once is necessary because no single kind of light reveals all of the energy and particle motion produced by an eruption.
Proxima Centauri is small and usually faint, but it can produce a powerful flare when stored magnetic energy is released all at once.
How do flares affect the atmospheres of nearby planets?
Proxima b and d orbit very close to their star. A flare of a given strength can therefore expose them to far more ultraviolet light and X-rays than Earth receives from the Sun. High-energy light can split atmospheric molecules, changing which gases are present and in what amounts. Over long periods, it can also help some of the atmosphere escape into space.
Strong flares, however, do not allow us to conclude immediately that an atmosphere or life is absent. The outcome depends on how often the flares occur, how many particles arrive, how thick the original atmosphere was and which gases it contained. A planet’s magnetic field and gases released from its interior may matter as well. No atmosphere has yet been detected directly around Proxima’s planets, so current studies compare how atmospheres would change under a range of possible conditions.
The figure of about 14,000 times the usual brightness refers to a brief ultraviolet peak measured in 2019. It does not mean that the star brightened by the same factor at every wavelength, including visible light, or remained that bright for long.
How can we distinguish stellar activity from a planet’s signal?
A planet’s gravity pulls Proxima slightly back and forth. This motion produces tiny differences in the star’s light as it moves toward and away from Earth. Starspots and bright regions can produce similar differences as the star rotates. Measurements taken during a flare cannot simply be treated in the same way as the star’s quiet light.
Researchers compare the star’s measured speed, brightness changes and magnetic activity across several kinds of light. A change caused by a planet should repeat with the same period over a long time. A signal that changes when starspots or flares grow stronger is treated as stellar activity and calculated separately. This is why Proxima b and d were checked with different instruments over long observing campaigns.
- Measure the star in its usual state Record its temperature and composition, rotation and baseline magnetic activity.
- Observe several kinds of light together Track how one flare differs in ultraviolet, visible and radio wavelengths.
- Identify changes caused by rotation Check whether starspots and bright regions return about every 90 days.
- Search separately for a planet’s period Test whether the distinct 11.2-day and 5.12-day cycles repeat in data from several instruments.
Can telescopes show us Proxima’s surface?
In Hubble images, Proxima Centauri appears as a bright point with a pattern of light rays, not as a resolved round stellar surface. Its actual disk is too small for a photograph to show where a starspot or flare occurred. Its mass, radius, temperature and rotation are calculated by combining measurements of distance, brightness and the colors in its light with stellar models.
The name “red dwarf” does not mean that people have seen a clearly red surface. It is a classification for a star cool enough to emit more long-wavelength light than the Sun. The star illustration on this page is a visualization based on measurements, not a photograph of the actual surface.
What else can we learn by observing such a nearby star?
A distance of 4.24 light-years is not within reach of a quick journey by present-day spacecraft, but Proxima appears brighter than more distant stars and is well suited to repeated measurements. Researchers can keep counting small flares, follow long-term changes in rotation and magnetic activity, and measure how much the planets make the star wobble. These observations show how activity in small red dwarfs can interfere with planet searches and affect the atmospheres of nearby planets.
Sources
- NASA Science — Proxima Centauri
- NASA — Alpha Centauri: A Triple Star System
- ESA — Proxima Centauri, Our Nearest Neighbour
- NASA Science — Neighboring Star’s Bad Behavior
- NASA Science — Puny Stars Pack a Big Punch
- Astronomy & Astrophysics — Proxima Centauri Stellar Parameters
- Astronomy & Astrophysics — Proxima Centauri with NIRPS