Image: NASA/JPL-Caltech How do scientists “see” black holes? Dr. Abbie Stevens 

First: what is astronomy? • Astronomy: stuff in outer space • Astrophysics: physics of stuff in outer space • Also: astrochemistry, astrobiology, heliophysics, Earth & planetary sciences, near-Earth space physics Image: NASA/ESA/HST Tools: math, computer programming, creative problem-solving, teamwork 

Black holes • A lot of stuff (mass) in a very small space • Very powerful gravity • Escape velocity faster than the speed of light! Image: J. Provost, ScienceNews.org 

Black holes Image: Event Horizon Telescope collaboration No limit on how big they can get! Small black holes are formed from the death and collapse of a big star (“stellar” or “stellar mass”) Big black holes have been around since very early in the universe, at the centers of galaxies (“supermassive”) 

Black holes Image: Event Horizon Telescope collaboration No limit on how big they can get! Small black holes are formed from the death and collapse of a big star (“stellar” or “stellar mass”) Big black holes have been around since very early in the universe, at the centers of galaxies (“supermassive”) Quick interlude: Universe is really big, numbers get really big 

Black holes Image: Event Horizon Telescope collaboration No limit on how big they can get! Small black holes are formed from the death and collapse of a big star (“stellar” or “stellar mass”) Big black holes have been around since very early in the universe, at the centers of galaxies (“supermassive”) Quick interlude: Universe is really big, numbers get really big 1 thousand seconds ≅ 16 minutes 

Black holes Image: Event Horizon Telescope collaboration No limit on how big they can get! Small black holes are formed from the death and collapse of a big star (“stellar” or “stellar mass”) Big black holes have been around since very early in the universe, at the centers of galaxies (“supermassive”) Quick interlude: Universe is really big, numbers get really big 1 thousand seconds ≅ 16 minutes 1 million seconds ≅ 11 days 

Black holes Image: Event Horizon Telescope collaboration No limit on how big they can get! Small black holes are formed from the death and collapse of a big star (“stellar” or “stellar mass”) Big black holes have been around since very early in the universe, at the centers of galaxies (“supermassive”) Quick interlude: Universe is really big, numbers get really big 1 thousand seconds ≅ 16 minutes 1 million seconds ≅ 11 days 1 billion seconds ≅ 32 years 

Black holes Image: Event Horizon Telescope collaboration Biggest black hole ever seen: 60 Billion times the mass of our Sun Smallest black hole ever seen: 3 times the mass of our Sun No limit on how big they can get! Small black holes are formed from the death and collapse of a big star (“stellar” or “stellar mass”) Big black holes have been around since very early in the universe, at the centers of galaxies (“supermassive”) 

Can’t just grab one, put it on a table, shine a light on it, and study it Video: NASA/GSFC/J. Schnittman Black holes To see it, need to wait for one to send light in our direction 

Image: Event Horizon Telescope collaboration How do we see them? taking a picture using radio light 

Image: Event Horizon Telescope collaboration How do we see them? taking a picture using radio light 

Image credit: NASA/CXC/M. Weiss How do we see them? eating its star-friend 

How do we see them? eating its star-friend Video credit: NASA 

The first black hole we saw is called Cygnus X-1, in 1972. How do we see them? eating its star-friend Image credit: NASA/CXC/M. Weiss 

Type of light Gets through Earth’s atmosphere? Approx. scale of wavelength? The electro-magnetic spectrum How do we see them? with X-ray telescopes The colors that we see are a very small part of all the types of light that exist! Images: Shutterstock, NASA 

The electro-magnetic spectrum How do we see them? with X-ray telescopes Type of light Gets through Earth’s atmosphere? Approx. scale of wavelength Images: Shutterstock, NASA X-rays from space can’t get through Earth’s atmosphere, so we put X-ray telescopes on satellites and launch them into space on rockets! 

Video: NASA/GSFC How do we see them? with X-ray telescopes 

Black hole as ☆ How do we see them? nearby orbiting stars Sagittarius A-star (Sgr A*) at the center of our Milky Way galaxy! 4.3 million times the mass of the Sun 

Image credit: NASA/CXC/M. Weiss How do we see them? smashing together Video: S. Ossokine/A. Buonanno/T. Dietrich (MPI for Gravitational Physics)/R. Haas (NCSA)/SXS project 

Image credit: NASA/CXC/M. Weiss Video: T. Ramirez/G. Lovelace/SXS Collaboration/LIGO-Virgo Collaboration How do we see them? smashing together 

How do we see them? bending light from behind them 

Image: HST How do we see them? bending light from behind them The strong gravity of the black hole acts like a lens, bending and distorting the image. 

Image credit: NASA/CXC/K. Divona 

Dr. Abbie in school • Middle school and high school: physics, earth science, math, computer programming 

• Middle school and high school: physics, earth science, math, computer programming • College: small liberal arts college • BA, physics major, math minor Dr. Abbie in school 

• Middle school and high school: physics, earth science, math, computer programming • College: small liberal arts college • BA, physics major, math minor • Graduate school: large research universities • MSc in physics, in astrophysics group Dr. Abbie in school 

• Middle school and high school: physics, earth science, math, computer programming • College: small liberal arts college • BA, physics major, math minor • Graduate school: large research universities • MSc in physics, in astrophysics group • PhD in astronomy, in large astronomy research institute Dr. Abbie in school 

•Middle school and high school: physics, earth science, math, computer programming •College: small liberal arts college •BA, physics major, math minor •Graduate school: large research universities •MSc in physics, in astrophysics group •PhD in astronomy, in large astronomy research institute In high school, I wanted to do architecture and engineering, so I took physics and math. Then in physics I was introduced to astronomy! • Learn about things that interest you, and keep an open mind! Dr. Abbie in school 

•Middle school and high school: physics, earth science, math, computer programming •College: small liberal arts college •BA, physics major, math minor •Graduate school: large research universities •MSc in physics, in astrophysics group •PhD in astronomy, in large astronomy research institute In high school, I wanted to do architecture and engineering, so I took physics and math. Then in physics I was introduced to astronomy! • Learn about things that interest you, and keep an open mind! In college, I changed majors twice! (environmental policy, theater), nearly added math as a double major • It’s ok to change your mind! Dr. Abbie in school 

•Middle school and high school: physics, earth science, math, computer programming •College: small liberal arts college •BA, physics major, math minor •Graduate school: large research universities •MSc in physics, in astrophysics group •PhD in astronomy, in large astronomy research institute In high school, I wanted to do architecture and engineering, so I took physics and math. Then in physics I was introduced to astronomy! • Learn about things that interest you, and keep an open mind! In college, I changed majors twice! (environmental policy, theater), nearly added math as a double major • It’s ok to change your mind! • Keep your hobbies! • Mental wellbeing is so important! Dr. Abbie in school 

Job prospects in astronomy • Academia • Researcher • Professor (research + teaching) • Lecturer/instructor (teaching) • Education and public outreach • Planetarium director • Outreach coordinator • Content at educational nonprofits • Industry • Data science • Quantitative analytics • Software development 

Image: NASA/JPL-Caltech Q&A time!