Astronomers from the University of Warsaw have discovered a Cepheid object with a record pulsation period in the Milky Way

Classic Cepheid stars are variable stars, pulsating giants that regularly change their brightness. They have found very important astrophysical applications. In 1924, the American astronomer Edwin Hubble used the relationship between the period of luminosity achieved by Cepheids to prove that the universe consists of countless galaxies and not, as previously thought, only the Milky Way. A few years later, observations of Cepheid stars in nearby galaxies helped Hubble discover that the universe was expanding, quickly leading to the formulation of the Big Bang theory.

Today, classical Cepheids are widely used to measure distances between galaxies and study the structure of galaxies. Among other things, Cepheids are the basis for the most precise measurement of the Hubble constant, the quantity that determines the expansion rate of the universe.

The newly identified star was given the catalog name OGLE-GD-CEP-1884. The Astronomical Observatory of the University of Warsaw said in a statement on Thursday that it pulsates with a period of 78.14 days, nearly 10 days longer than the pulsation period of the previous record holder.

The discovery was made by scientists working as part of the OGLE project conducted at the observatory. The star was chosen by Professor Igor Soszynski, a world leader in research into variable stars.

“So far, no ULPC-type object has been known in our galaxy, although most galaxies studied contain many Cepheid stars of this type. The star OGLE-GD-CEP-1884, although brighter by more than 25,000 times that of the star Cepheid.” The Sun, has not previously been properly classified as a Cepheid because it lies behind a thick layer of interstellar material that absorbs light coming from the object, especially in the blue part of the spectrum,” we read in the statement. Many years of optical observations of this star, conducted by The OGLE team's work on the red light, combined with radial velocity measurements made by the Gaia Space Telescope, allowed us to clearly establish that it is a classic Cepheid star.

“The discovery of this object indicates that the Milky Way is not unique among other galaxies in terms of the occurrence of long-period Cepheid stars, and it is likely that the current lack of observations of this type of star in our Galaxy is due to the fact that ULPCs are The stars are obscured by thick clouds of interstellar dust. OGLE-GD-CEP-1884 is not only the brightest Cepheid star, but also the youngest known classical Cepheid star in the Milky Way. Its age is estimated at 22 million years.

According to the researchers, using the relationship of the brightness period of Cepheids, it was possible to measure the distance to OGLE-GD-CEP-1884 and determine its location on the map of our Galaxy. This star is located 14,500 light-years away in the carbon spiral arm among the relatively young classical Cepheid stars. The discovery of OGLE-GD-CEP-1884 will contribute to a more precise calibration of the relationship between the luminosity period of Cepheids and to a better understanding of the evolution of massive stars.

The newly discovered star OGLE-GD-CEP-1884 belongs to a small group of Cepheid stars with extremely long pulsation periods. Cepheids are long lasting(abbreviated as ULPC). One of the features of this type of object – as astronomers from the University of Warsaw explained – is its high brightness, which is used to measure the distance to galaxies that are up to 300 million light-years away from us.

The OGLE research team led by Prof. Andrzej Udalski has extensive experience in discovering and studying pulsars. Almost half of all classical Cepheid elements currently known in the Milky Way have been discovered by astronomers from the University of Warsaw – as we mentioned in the release.

A few years ago, researchers led by Prof. Dorota Skowron has published a 3D map of our Galaxy, obtained on the basis of the spatial distribution of Cepheids discovered by the OGLE team. This map clearly showed that the disk of the Milky Way Galaxy is not flat, but rather curved in an S-shape.