A planetary nebula called the Stingray Nebula has faded precipitously over just the past 20 years, according to an analysis of the archival images from the NASA/ESA Hubble Space Telescope.
These images of the Stingray Nebula were captured by Hubble in 1996 (left) and 2016 (right). Image credit: NASA / ESA / B. Balick, University of Washington / M. Guerrero, Instituto de Astrofísica de Andalucía / G. Ramos-Larios, Universidad de Guadalajara.
The Stingray Nebula, the youngest known planetary nebula, is located 2,700 light-years away in the southern constellation of Ara.
Also known as Hen 3-1357, the nebula is some 130 times the size of our Solar System.
The Stingray Nebula’s central star, designated SAO 244567, was classified as an A- or B-type star in 1967.
Typical planetary nebula emission lines were unexpectedly detected from SAO 244567 in 1990.
Hubble images taken in 1992 and 1996 first revealed the compact planetary nebula.
In 2016, University of Leicester astronomer Nicole Reindl and colleagues noted that SAO 244567 is special in its own right.
Observations from 1971 to 2002 showed the temperature of the star skyrocketing to almost 10 times hotter than the surface of our Sun.
The researchers speculated that the temperature jump was caused by a brief flash of helium fusion that occurred outside the core of the central star.
After that the star began to cool again, returning to its previous stage of stellar evolution.
“In most studies, the nebula usually gets bigger,” said University of Washington’s Dr. Bruce Balick, lead author of the current study.
“Here, it’s fundamentally changing its shape and getting fainter, and doing so on an unprecedented timescale.”
Dr. Balick and colleagues analyzed archival images of the Stingray Nebula obtained by Hubble in 1996, 2000, and 2016, and found that the nebula has drastically dimmed in brightness and changed shape.
Bright blue shells of gas near its center have all but disappeared, and the wavy edges that earned this nebula its aquatic-themed name are virtually gone.
The young nebula no longer pops against the black velvet background of the distant Universe.
The scientists also discovered unprecedented changes in the light emitted by glowing gas — nitrogen, hydrogen and oxygen — that is being blasted off by SAO 244567.
The oxygen emission, in particular, dropped in brightness by a factor of nearly 1,000.
“Because of Hubble’s optical stability, we are very, very confident that this nebula is changing in brightness,” said Dr. Martin Guerrero, an astronomer in the Instituto de Astrofísica de Andalucía.
“That easy to see since, unlike the nebula, all of the other stars in the Hubble image — including a distant companion star — stayed constant in brightness.”
The findings will be published in the Astrophysical Journal.
_____
Bruce Balick et al. 2020. The Fall of the Youngest Planetary Nebula, Hen3-1357. ApJ, in press; arXiv: 2009.01701
