L'Italo-Americano

L'Italo-Americano THURSDAY, AUGUST 24 2023 www.italoamericano.org 4 S h e d i s c o v e r e d a star and named it J a n u s , a f t e r t h e a n c i e n t R o m a n deity of gates and doors, a mythological figure depicted with two faces. Ilaria Caiazzo, a theoret- ical astrophysicist from Italy who works at the California Institute of Technology (Cal- tech) in Pasadena, was in charge of the team that led to the discovery of a star - called a white dwarf - that, like Janus, has the characteristic o f h a v i n g t w o f a c e s , o n e made of hydrogen and one of h e l i u m . " T h e y a r e c a l l e d dwarfs because they are very s m a l l , " C a i a z z o e x p l a i n s . "And white because when they were found they were not very bright, especially if you think that stars tend to b e r e d d e r t h a n t h e s u n . W h i t e d w a r f s a r e t h e l a s t s t a g e i n t h e e v o l u t i o n o f s m a l l - a n d m e d i u m - m a s s stars." 34, born in Piedmont and raised in Savona, Liguria, a f t e r s t u d y i n g p h y s i c s between Genoa and Milan, and after a doctorate at the University of British Colum- bia in Vancouver, Caiazzo arrived at Caltech in Pasade- na with a Bruke Prize Fellow- ship in October 2019. "At Caltech, I mainly work on star corpses. When a star runs out of hydrogen or heli- um and has no way to burn, it stops producing energy and b e c o m e s a ' w h i t e d w a r f . ' What determines how long a star lives is its mass: smaller stars live longer, larger stars have more material to burn but burn it faster. A star larg- er and brighter than the sun lives about 100 million years. The sun will live 10 billion years". T a k i n g a s t e p b a c k , what is a star from a sci- entific point of view and how do they differ from each other? A star is a cluster of gas that burns by nuclear fusion in its center. Stars differ in mass: for example, the Sun is a small star, while there are stars that have a mass 50 times greater than that of the Sun. At around 1/10th of the Sun's mass, stars are too low i n m a s s a n d c a n n o t f e e d themselves. Tell us about your dis- covery. Janus is a white dwarf, that is, a cadaver star like the Sun; however, the parent of this star was at least seven times the size of the Sun. I discovered it using a tele- scope located at the Mount Palomar Observatory in San Diego, the Zwicky Transient Facility, a telescope built in t h e 1 9 4 0 s , w h i c h p h o - tographs the sky every night, managing to cover almost the entire Northern Hemi- sphere. It was built to find t h i n g s t h a t e x p l o d e a n d detect what's new by com- p a r i n g i m a g e s b e t w e e n them. I observed it many t i m e s a f t e r w a r d a s w e l l , because when you discover something so strange you want to make sure it is true. I observed it with different telescopes. How many telescopes have you used? A t M o u n t P a l o m a r i n a d d i t i o n t o t h e t e l e s c o p e from the 1940s, which is 48 inches wide and two meters or so in length, there is also another 5-meter telescope, also built in the 1940s and called The Big Eye. I also used the Keck Observatory in Hawaii, on Big Island. T h e r e ' s a l s o a t e l e s c o p e t h a t ' s i n s p a c e , t h e S w i f t Telescope, that can see ultra- violet rays and therefore can confirm temperature; I also used a telescope in Las Pal- m a s , C a n a r y I s l a n d . A n d finally ... it all added up! How old is Janus and what are its characteris- tics? We do not know the age of Janus. The fact that it rotates so fast suggests it is the result of two stars that merged together. Its age is probably 1 billion years. A few years ago you d i s c o v e r e d a n o t h e r white dwarf, the small- est ever observed, and now Janus, a two-sided w h i t e d w a r f . W h a t sparked your interest in this type of star? I b e c a m e i n t e r e s t e d i n finding white dwarfs that change in brightness period- ically; my interest was find- ing magnetic white dwarfs that rotate on themselves. Several years ago, I pub- l i s h e d a p a p e r i n N a t u r e because I had found a white dwarf that rotated on itself e v e r y 7 m i n u t e s w i t h i n a very strong magnetic field. C o n s i d e r t h a t t h e E a r t h rotates on itself every 24 h o u r s , t h e S u n e v e r y 2 7 days, and white dwarfs every few hours. This information is valuable because it tells us w h i t e d w a r f s a r e n o t t h e daughters of one star but of t w o . S t a r s a r e o f t e n i n a binary pair: if both become white dwarfs and if they are c l o s e e n o u g h , t h e y e m i t gravitational waves (gravita- tional waves were discovered at Caltech in 2015, a discov- ery that later led Kip Thorne, Ray Weiss and Barry Barish to win the Nobel Prize) that c a r r y a w a y e n e r g y , s o i n such a situation, the orbits get smaller and smaller until they collide. This happens for all stellar corpses and also for white dwarfs. These super-magnetic objects are almost certainly the result of a merger between two white dwarfs. What do we still not know about stars? Many things, such as how many stars there are and how they merge together. In some cases, white dwarfs m e r g e , i n o t h e r s , t h e y explode into a supernova. Supernovae are very impor- tant in astronomy because they allow us to measure the distance and expansion of the universe. How did your passion f o r t h e s t a r s c o m e about? I t d o e s n ' t c o m e f r o m childhood like it usually hap- pens. In my family, no one works in the field of science. In college I enrolled in phi- losophy, then I moved to physics, and later I moved from particle physics to the- oretical physics. So, I came to astronomy following an unusual path. When I stud- ied philosophy I was inter- e s t e d i n m e t a p h y s i c s , i n questions like: where do we c o m e f r o m , w h o a r e w e , what is time, what is space... so the move to physics was also because of that, because t h e s e a r e q u e s t i o n s t h a t quantum physics also asks. D i d y o u g e t t h o s e answers? N o , a b s o l u t e l y n o t . I a s k e d m y s e l f e v e n m o r e q u e s t i o n s . B u t s t u d y i n g physics helped me under- stand what questions I need to ask myself. Is there anything that surprised you from this point of view? In the 1800s they believed e v e r y t h i n g c o u l d b e explained mechanically with laws of physics, and then in the 1900s quantum mechan- ics came along and turned everything upside down. We realized the laws of physics are true and work but that we cannot understand them, they are beyond our under- standing. D o y o u c o l l a b o r a t e with any Italian entities? I am part of a team at this telescope called IXPE, the Imaging X-ray Polarimetry Explorer, a space observato- ry based on the collaboration b e t w e e n A S I a n d t h e U S Space Agency. The observa- tory consists of three tele- scopes designed for studies b a s e d o n c o s m i c X - r a y polarimetry. With this, we study neutron stars, another type of star corpses. What are your plans for the future? I will be at Caltech until May 2024. Then I'm moving to Vienna where I won a pro- f e s s o r s h i p a t a r e s e a r c h institute, founded in 2009, t h a t i s e s t a b l i s h i n g a n astronomy group. I will be teaching and doing research. It is an international center with several departments: neuroscience, computer sci- ence, chemistry, etc. They want to expand, there are 75 g r o u p s a n d t h e y w a n t t o grow to 150 in the next ten years. Caltech: Italian scientist discovers two-faced white dwarf SILVIA NITTOLI NEWS & FEATURES TOP STORIES PEOPLE EVENTS Italian astrophysicist Ilaria Caiazzo (Photo: Jakub Ostrowski Photography)

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