Just in time for Valentine’s Day, space offers a heart-shaped greeting. The star Mira A, about 300 light-years from Earth, has released material into an expanding cloud of gas and dust resembling a heart. Both the amount of material and the speed at which the star ejected it were unexpected.
“We were very surprised to see this structure. We also see that the star’s illumination of the surrounding dust varies in an unexpected way, which implies that the star acts like a lighthouse – illuminating its environment unevenly”, says Theo Khouri, Chalmers astronomer and lead author of the new study.
Mira A is a well-known star, with its first documented observation as far back as 1596. As a red giant star in the last stages of its life cycle, it ejects dust and gas into the surrounding environment. A team of astronomers led by Theo Khouri, Chalmers, discovered two large clouds of material expanding away from Mira A while analyzing observations of the star acquired between 2015 and 2023. The large amount of material – roughly a hundred times more than expected, or equivalent to seven times the mass of the Earth – drew the attention of the team. They studied the ejected material in detail to better understand how the mass-loss mechanism works for this type of star.
“We know that stars like Mira lose mass as they age, but we did not expect it to happen in such large and sudden bursts,” says Theo Khouri.
Combined observations revealed the structure
To examine the star and its surrounding material, the researchers used observations from both the European Southern Observatory's VLT (ESO's Very Large Telescope) and ALMA (Atacama Large Millimeter/submillimeter Array) in Chile, in visible light as well as at radio frequencies. Observations spanning several years revealed how gas fills the heart-shaped structure, while dust is concentrated along its edges, forming a glowing outline.
The discovery provides new insights into how ageing stars evolve and shed material that later becomes the building blocks of new stars and planets. It is presented in the study A surprisingly large asymmetric ejection from Mira A, by Theo Khouri, et al, accepted for publication in Astronomy and Astrophyics.
“We will keep monitoring the expanding cloud around Mira A, as it is becoming so large that it may start to affect its companion star, the white dwarf Mira B. It is already gathering some of the material ejected by Mira A”, says Theo Khouri, who also is part of the team of astronomers who presented two widely publicized studies about the red giant star R Doradus: Stardust study resets how life’s atoms spread through space, and Unique images show gas bubbles on red giant star's surface.
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The first confirmed observation of the Mira star system was done as early as 1596 and consists of a red giant star – Mira A – and its white dwarf companion – Mira B. It is part of the constellation Cetus, often referred to as the Whale. Mira A is a variable star, whose surface pulsates, causing it to increase and decrease in brightness. Old red stars that pulsate like this are actually known as Mira variables, named after Mira A itself. The image of the Mira star system was ESO's picture of the week in 2014.
The team used the telescopes ALMA (Atacama Large Millimetre/submillimetre Array) and the Very Large Telescope (VLT), both located in Chile. The VLT is operated by ESO, the European Southern Observatory. Sweden is one of ESO’s 16 member states. Alma is a partnership of ESO (representing its member states, among them Sweden), NSF (USA) and NINS (Japan), together with NRC (Canada), NSTC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ.
Contacts:
- Researcher, Astronomy and Plasma Physics, Space, Earth and Environment
