ESO: First detection of Lithium ejected from a nova

A new report from ESO (European Southern Observatory):

First Detection of Lithium from an Exploding Star

The chemical element lithium has been found for the first time in material ejected by a nova. Observations of Nova Centauri 2013 made using telescopes at ESO’s La Silla Observatory, and near Santiago in Chile, help to explain the mystery of why many young stars seem to have more of this chemical element than expected. This new finding fills in a long-missing piece in the puzzle representing our galaxy’s chemical evolution, and is a big step forward for astronomers trying to understand the amounts of different chemical elements in stars in the Milky Way.

This image from the New Technology Telescope at ESO’s La Silla Observatory shows Nova Centauri 2013 in July 2015 as the brightest star in the centre of the picture. This was more than eighteen months after the initial explosive outburst. This nova was the first in which evidence of lithium has been found. Credit: ESO

The light chemical element lithium is one of the few elements that is predicted to have been created by the Big Bang, 13.8 billion years ago. But understanding the amounts of lithium observed in stars around us today in the Universe has given astronomers headaches. Older stars have less lithium than expected [1], and some younger ones up to ten times more [2].

Since the 1970s, astronomers have speculated that much of the extra lithium found in young stars may have come from novae — stellar explosions that expel material into the space between the stars, where it contributes to the material that builds the next stellar generation. But careful study of several novae has yielded no clear result up to now.

Alpha and Beta Centauri, two of the brightest stars in the southern sky, had a new companion in late 2013 — the naked eye Nova Centauri 2013. This photo was taken by ESO Photo Ambassador Yuri Beletsky at ESO's La Silla Observatory in the Chilean Atacama Desert in the morning hours of Monday 9 December 2013. The nova was discovered by John Seach from Australia on 2 December 2013 as it approached naked eye brightness. Nova Centaurus 2013 is the brightest nova to have occurred so far this millennium. This particular event is known as a classical nova, and is not to be confused with a supernova. Classical novae occur in binary star systems when hydrogen gas from the orbiting stellar partner is accreted onto the surface of the main star, causing a runaway thermonuclear event resulting in the brightening of the main star. In a classical novae the main star is not destroyed as is the case in a supernova. Instead, the star is dramatically brightened, and there is a simultaneous expansion of a debris shell. The nova appears in the picture just to the left of Beta Centauri, the bluer and higher of the two bright stars in the lower-right part of the image. The Southern Cross and the Coal Sack Nebula are also captured near the top of the picture. In front at the left is the ESO 3.6-metre telescope, inaugurated in 1976, it currently operates with the HARPS spectrograph, the most prolific exoplanet hunting machine in the world. Located 600 km north of Santiago, at 2400 m altitude in the outskirts of the Chilean Atacama Desert, La Silla was first ESO site in Chile and the largest observatory of its time. Links Image of Nova Centauri 2013 (non-annotated) — Alpha and Beta Centauri, two of the brightest stars in the southern sky, had a new companion in late 2013 — the naked eye Nova Centauri 2013. This photo was taken by ESO Photo Ambassador Yuri Beletsky at ESO’s La Silla Observatory in the Chilean Atacama Desert in the morning hours of Monday 9 December 2013. The nova was discovered by John Seach from Australia on 2 December 2013 as it approached naked eye brightness. Nova Centaurus 2013 is the brightest nova to have occurred so far this millennium. This particular event is known as a classical nova, and is not to be confused with a supernova. Classical novae occur in binary star systems when hydrogen gas from the orbiting stellar partner is accreted onto the surface of the main star, causing a runaway thermonuclear event resulting in the brightening of the main star. In a classical novae the main star is not destroyed as is the case in a supernova. Instead, the star is dramatically brightened, and there is a simultaneous expansion of a debris shell. The nova appears in the picture just to the left of Beta Centauri, the bluer and higher of the two bright stars in the lower-right part of the image. The Southern Cross and the Coal Sack Nebula are also captured near the top of the picture. In front at the left is the ESO 3.6-metre telescope, inaugurated in 1976, it currently operates with the HARPS spectrograph, the most prolific exoplanet hunting machine in the world. Located 600 km north of Santiago, at 2400 m altitude in the outskirts of the Chilean Atacama Desert, La Silla was first ESO site in Chile and the largest observatory of its time. Links Image of Nova Centauri 2013 (non-annotated)

A team led by Luca Izzo (Sapienza University of Rome, and ICRANet, Pescara, Italy) has now used the FEROS instrument on the MPG/ESO 2.2-metre telescope at the La Silla Observatory, as well the PUCHEROS spectrograph on the ESO 0.5-metre telescope at the Observatory of the Pontificia Universidad Catolica de Chile in Santa Martina near Santiago, to study the nova Nova Centauri 2013 (V1369 Centauri). This star exploded in the southern skies close to the bright star Beta Centauri in December 2013 and was the brightest nova so far this century — easily visible to the naked eye [3].

The very detailed new data revealed the clear signature of lithium being expelled at two million kilometres per hour from the nova [4]. This is the first detection of the element ejected from a nova system to date.

This video sequence starts from a wide field view of the Milky Way and closes in on the bright and famous pair of stars Alpha and Beta Centauri. Nova Centauri 2013 exploded close to Beta Centauri in the sky in late 2013 and careful study of the light from this star has revealed the first traces of the element lithium ever found in a nova. The final image in the zoom is a closeup of the nova taken using the New Technology Telescope at ESO’s La Silla Observatory in July 2015. The nova is the brightest star close to the centre of the picture and is much fainter than it was at maximum light, when it could be seen with the naked eye.

Credit: ESO/Digitized Sky Survey 2/N. Risinger (skysurvey.org). Music: Johan B. Monell (www.johanmonell.com).

Co-author Massimo Della Valle (INAF–Osservatorio Astronomico di Capodimonte, Naples, and ICRANet, Pescara, Italy) explains the significance of this finding:

“It is a very important step forward. If we imagine the history of the chemical evolution of the Milky Way as a big jigsaw, then lithium from novae was one of the most important and puzzling missing pieces. In addition, any model of the Big Bang can be questioned until the lithium conundrum is understood.”

The mass of ejected lithium in Nova Centauri 2013 is estimated to be tiny (less than a billionth of the mass of the Sun), but, as there have been many billions of novae in the history of the Milky Way, this is enough to explain the observed and unexpectedly large amounts of lithium in our galaxy.

This chart shows the location of Nova Centauri 2013 (red circle) in the constellation of Centaurus (The Centaur). All the stars easily seen with the naked eye on a dark clear night are shown. The nova erupted in late 2013 and was visible without a telescope. Careful study of the light from this nova has revealed the first traces of the element lithium ever found in a nova.

Authors Luca Pasquini (ESO, Garching, Germany) and Massimo Della Valle have been looking for evidence of lithium in novae for more than a quarter of a century. This is the satisfying conclusion to a long search for them. And for the younger lead scientist there is a different kind of thrill:

“It is very exciting,” says Luca Izzo, “to find something that was predicted before I was born and then first observed on my birthday in 2013!”