Cracking the Case of Cosmic Ghost Stars

Uncovering the missing out on precursors of hydrogen-poor supernovae.

Supernovae– outstanding surges as brilliant as a whole galaxy– have actually interested us because time immemorial. Yet, there are more hydrogen-poor supernovae than astrophysicists can describe. Now, a brand-new Assistant Professor at the Institute of Science and Technology Austria (ISTA) has actually played a critical function in determining the missing out on precursor star population. The results, now released in Science, return to a discussion the included teachers had several years back as junior researchers.

The Enigma of Hydrogen-Poor Supernovae

Some stars do not merely wane, however blow up in an excellent blast that might beat whole galaxies. These cosmic phenomena, called supernovae, spread out light, aspects, energy, and radiation in area and send out stellar shock waves that might compress gas clouds and produce brand-new stars. In other words, supernovae shape our universe. Among these, hydrogen-poor supernovae from blowing up enormous stars have actually long puzzled astrophysicists. The factor: researchers have actually not had the ability to put their finger on their precursor stars. It is practically as if these supernovae appeared out of no place.

“There are many more hydrogen-poor supernovae than our current models can explain. Either we can’t detect the stars that mature on this path, or we must revise all our models,” states ISTA Assistant Professor Ylva Götberg. She originated this interact with Maria Drout, an Associated Faculty Member of the Dunlap Institute for Astronomy & &(******************************************************************************************************************************************************************************************************************************************************** )(********************************************************************************************************************* )of Toronto, Canada.

“Single stars would typically explode as hydrogen-rich supernovae. Being hydrogen-poor indicates that the precursor star must have lost its thick hydrogen-rich envelope. This happens naturally in a third of all massive stars through envelope stripping by a binary companion star,” states Götberg.

Now, Götberg and Drout integrated their locations of competence in theoretical modeling and observation to hound the missing out on stars. Their mission achieves success: they record a first-of-its-kind star population that lastly bridges a big understanding space and clarifies the origin of hydrogen-poor supernovae.

Binary Stars and Envelope Stripping

The stars that Götberg and Drout look for go in sets: interlocked in a binary star system. Some double stars are popular to us Earthlings: these consist of the brightest star in our night sky, Sirius A, and its faint buddy star Sirius B. The Sirius double star lies just 8.6 light-years far from Earth– a stone’s include cosmic terms. This discusses Sirius A’s observed brightness in our night sky.

Astrophysicists anticipate the missing out on stars to be at first formed from enormous double stars. In a double star, the stars would orbit around one another till the more enormous star’s thick, hydrogen-rich envelope expands. Eventually, the broadening envelope experiences a more powerful gravitational pull to the buddy star than to its own core.

This triggers a transfer of mass to start, which ultimately leads the whole hydrogen-rich envelope to be removed off, leaving the hot and compact helium core exposed– more than 10 times hotter than the Sun’s surface area. This is specifically the kind of stars that Götberg and Drout are searching for.

A three-panel artist’s impression of a star being removed by a binary buddy. The 3rd panel illustrates the phase when these stars are observed in today work. Stills from a motion picture. Credit: © ESO/L. Cal çada/ M. Kornmesser/ S.E. de Mink

“Intermediate mass helium stars stripped through binary interaction are predicted to play important roles in astrophysics. Yet, they were not observed until now,” states Götberg.

In truth, there is a crucial mass space in between the recognized classes of helium stars: the more enormous Wolf-Rayet (WR) stars have more than 10 times the Sun’s mass, and the low-mass subdwarf stars might have around half the Sun’s mass. However, designs have actually anticipated the precursors of hydrogen-poor supernovae to lie in between 2 and 8 solar masses following removing.

Not Just a Needle in the Haystack

Before Götberg and Drout’s research study, just one star was discovered to satisfy the anticipated mass and structure requirements and was called “Quasi-WR” (or “Almost Wolf-Rayet”).

“Yet, the stars that follow this path have such a long lifetime that many must be scattered all over the observable universe,” states Götberg.

Did the researchers merely not “see” them? Thus, Götberg and Drout made use of their complementary competence. With the assistance of UV photometry and optical spectroscopy, they recognized a population of 25 stars that follow the expectations for intermediate-mass helium stars. The stars lie in 2 well-studied surrounding galaxies, the Large and the Small Magellanic Clouds.

“We showed that these stars were bluer than the stellar birthline, the bluest phase in a single star’s lifetime. Single stars mature by evolving towards the redder region of the spectrum. A star only shifts in the opposite direction if its outer layers are removed–something that is expected to be common in interacting binary stars and rare among single massive stars,” discusses Götberg.

Study authors Bethany Ludwig, Anna O’Grady, Maria Drout and Ylva Götberg observing on the Magellan telescopes at Las Campanas Observatory in Chile, where they collected information for this research study. Credit: Y. Götberg

The researchers then validated their prospect star population utilizing optical spectroscopy: they revealed that the stars had strong spectral signatures of ionized helium.

“Strong ionized helium lines tell us two important things: first, they confirm that the stars’ outermost layers are dominated by helium and, second, that their surface is very hot. This is what happens to stars left as an exposed, compact, helium-rich core following stripping,” states Götberg.

Yet, both stars in a double star add to the observed spectra. Thus, this method enabled the scientists to categorize their prospect population depending upon which star contributed the most to the spectrum.

“This work allowed us to find the missing population of intermediate-mass, stripped helium stars, the predicted progenitors of hydrogen-poor supernovae. These stars have always been there and there are probably many more out there. We must simply come up with ways to find them,” states Götberg. “Our work may be one of the first attempts, but there should be other ways possible.”

From Graduate Students to Leaders in Astrophysics

The concept behind this task triggered in a conversation following a talk by Götberg at a conference that she and Drout went to throughout their graduate research studies. Both researchers, then Early Career Researchers grabbing the stars, are now group leaders in their field.

Götberg signed up with ISTA in September following her research study at the Carnegie Observatories in Pasadena, California, as a < period class ="glossaryLink" aria-describedby ="tt" data-cmtooltip ="<div class=glossaryItemTitle>NASA</div><div class=glossaryItemBody>Established in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. Its vision is &quot;To discover and expand knowledge for the benefit of humanity.&quot; Its core values are &quot;safety, integrity, teamwork, excellence, and inclusion.&quot; NASA conducts research, develops technology and launches missions to explore and study Earth, the solar system, and the universe beyond. It also works to advance the state of knowledge in a wide range of scientific fields, including Earth and space science, planetary science, astrophysics, and heliophysics, and it collaborates with private companies and international partners to achieve its goals.</div>" data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]" tabindex ="0" function ="link" > NASA(**************************** )Hubble postdoctoral fellow.At ISTA, Götberg signs up with theInstitute’s growing ranks of young group leaders in astrophysics and leads her own group concentrated on studying the binary interactions of stars.

Reference:“An observed population of intermediate-mass helium stars that have been stripped in binaries” by M. R.Drout, Y. Götberg, B. A.Ludwig, J. H.Groh, S. E. deMink, A. J. G. O’Grady and N.Smith,14December2023,Science
DOI:101126/ science.ade4970

This work, led byMaria R.Drout(DunlapInstitute forAstronomy &Astrophysics,University ofToronto,Canada) andYlva Götberg(Institute of(****************************************************************************************************************************************************** )and Technology Austria, ISTA), was performed in partnership with The Observatories of the < period class ="glossaryLink" aria-describedby ="tt" data-cmtooltip ="<div class=glossaryItemTitle>Carnegie Institution for Science</div><div class=glossaryItemBody>The Carnegie Institution for Science is a private, nonprofit organization based in Washington, D.C. that conducts scientific research and education. It was founded in 1902 by Andrew Carnegie and is one of the oldest independent research institutions in the United States. The Carnegie Institution for Science includes six research departments: Embryology, Observatories, Plant Biology, Global Ecology, Terrestrial Magnetism, and DTM (Department of Terrestrial Magnetism). It also has a number of affiliated programs and initiatives, including the Carnegie Academy for Science Education and the Carnegie Institution for Science&#039;s Department of Global Ecology.</div>" data-gt-translate-attributes ="[{"attribute":"data-cmtooltip", "format":"html"}]" tabindex ="0" function ="link" >CarnegieInstitution forScience(Pasadena, U.S.A.), and theMaxPlanckInstitute forAstrophysics(Garching,Germany), to name a few.