The Milky Way Galaxy

Our Home, the Milky Way Galaxy

Dr. Sean Carey (IPAC) Dr. Dan Patnaude (CfA) Dr. Jessie Christiansen (IPAC) Universe of Learning science briefing Dr. Seth Digel (SLAC) August 25, 2016 1 Planets and Moons

2 Stars

3 Gas and Dust

4 Black Hole 5 Star Formation and the Structure of the Milky Way

Sean Carey (IPAC/Caltech) 6 6 Structure of Galaxies

M51 M83 LMC

Andromeda IC 2006 Arp 220

Galaxies show a wide range of shapes based on their history and environment NGC 1300 7 Images courtesy ESA and STScI Our View of the Milky Way

Death Valley / NPS

The Sun is in the midplane of our Galaxy about 1/3rd of the distance out from the center, but what does our Galaxy really look like?

8 8 ISS / NASA Being in the Galaxy is a Tough Vantage Point

Side View from roof of Spitzer Science Center looking towards Rose Bowl

Rose Bowl Aerial View of Pasadena – courtesy of Google Maps

Spitzer Science Center 9

Interstellar dust absorbs and scatters light just like smog in LA

Donovan

Blue Red Infrared Blue/Red/Infrared

Redder light is blocked less: You can see through most of the murk in the infrared 10 Going from 2d to 3d : Turning Pictures into a Galactic Map

There are no rulers that can be observed in our Galaxy.

But there are types of stars called Red Clump Giants for which we know the intrinsic brightness. They are also fairly common and bright and can be used to trace the structure of the Galaxy.

These can be used to measure distances; stars twice as far away are four times fainter.

A portion of a Spitzer Space Telescope Map of the plane of our Galaxy 11 The Milky Way

Our Galaxy is thought to be a barred spiral galaxy; the shape of the Galaxy on the other side is not really well known 12 Stellar Birth and Citizen Science https://www.milkywayproject.org/

http://www.spitzer.caltech.edu/glimpse360 Newly forming stars heat up the surrounding gas and dust that they form out of, causing the dust to glow brightly in the infrared 13 Stellar Old Age (and Death)… and Citizen Science

Aging and dying stars throw off shells of gas and dust that glow in the Infrared images of shells from the infrared Spitzer Space Telescope 14 Summary and Future • Mapping of our Galaxy in the infrared using the Spitzer Space Telescope (and the Herschel Space Telescope) has informed us about the structure of our Galaxy and the lifecycle of stars (in particular how they form and what happens when they die) • The maps of our Galaxy answer many questions in NASA’s Cosmic Origins program • Future studies of star formation will be conducted with the James Webb Telescope which will provide a more detailed view of the process • Future mapping of the structure of our Galaxy will be done by WFIRST which will make the first stellar map of the far side of the Galaxy • All of these programs have greatly benefitted from citizen scientists who have made many discoveries by examining the large maps of the Galactic plane produced with Spitzer

A snake-like shaped region where stars are forming 15 Supernovae and Supernova Remnants

Dan Patnaude Harvard-Smithsonian Center for Astrophysics

- lifecycles of stars

Credit: NASA/CXC Credit: 17 - lifecycles of stars

18 - Example Supernova: SN 1987A

After Before

19 - the electromagnetic spectrum

20 - the structure of supernovae and their remnants

Credit: Dan Patnaude (Harvard-Smithsonian Center for Astrophysics) 21

- the structure of supernovae and their remnants

Credit: Pat Slane (CXC/Smithsonian) 22 - Example Supernova Remnant: Kepler’s SNR (SN 1604)

Credit: NASA/CXC 23 - Example Supernova Remnant: Cassiopeia A

Credit: NASA/CXC 24 - Example Supernova Remnant: Cassiopeia A - viewed in hard X-rays

Credit: NASA/NuSTAR/CalTech

25 Summary

• Supernova represent the violent endpoints in the evolution of some stars - they are responsible for the formation of heavy elements, and in particular the bulk of the metals that we observe in the universe - some supernova remnants are responsible for accelerating particles up to very high energies. We see evidence for this in the acceleration of electrons by highly amplified magnetic fields found in supernova shocks - by combining data from several NASA missions such as Chandra and NuSTAR, we are able to test theories for the evolution of massive stars as well as theories for the synthesis of heavy elements in supernova explosions, thus addressing fundamental questions posed by NASA in relation to how the universe works

26 EXOPLANETS

Image credit: NASA/JPL

Jessie Christiansen, NASA Exoplanet Science Institute 27 What are exoplanets?

Artist’s rendering: NASA. Orbits not to scale. 28 How do we find them?

NASA NASA

Planets pull on their host stars Planets block the light from their host stars … this tells us their mass … this tells us their size In the last 21 years we have found over 3370 exoplanets! 29 What have we found?

NASA/IAU

30 So many surprises…

A planet where it rains liquid glass...

Planets orbiting two – or even three! – stars...

An egg-shaped planet, distorted by its host star...

Orphaned planets, floating free in interstellar space…

Planets being disintegrated by their host stars...

Newborn planets only a few million years old...

But no Earth twins... Yet!

31 Where are we finding them?

(http://eyes.jpl.nasa.gov/eyes-on-exoplanets.html) 32 How common are planets?

1 3 of stars like the Sun have planets 33 The Milky Way is Full of Exoplanets!

Studying exoplanets helps us to answer many of humanity’s, and NASA’s, biggest questions

How did we get here?

Are we Alone?

NASA 34 Center of the Milky Way

Optical photomosaic (A. Mellinger) Studying the Galactic Center outside the visible spectrum

Seth Digel (KIPAC/SLAC) Universe of Learning Briefing 25 August 2016

35 Finding the Galactic Center To Earth

Until the 1950s the accepted location of the GC was off by >30 degrees!

Radio astronomy allowed mapping of interstellar gas dynamics

The direction of the GC is now known extremely precisely: Sagittarius A*

Rougoor & Oort (1959) 36 Sagittarius A* is a Massive Black Hole Keck Near Infrared Observations of Stellar Orbits around Sgr A* Tracking motions of individual massive stars in orbit around it has allowed its mass to be estimated (~4 million solar masses)

Implied density confirms its black hole nature

~0.1 light year

37 Active Galactic Nuclei

So-called active galaxies have intense, Composite image of Centaurus A variable, ‘non-thermal’ emission Active Galaxy associated with accretion disks of matter around their central black holes

Depending on the wavelength and direction, this nuclear emission can dominate the output of the entire galaxy

A related phenomenon is nuclear jets of high-energy particles

Centaurus A is a relatively nearby ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. example (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)

38 Milky Way is a Sort-of Active Galaxy

A weak jet interacting with ionized gas in the inner few light years

VLA radio observations Chandra X-ray observations

Jet feature is ~3 light years long

Li et al. (2013)

But the Milky Way may have been more active in the past… 39 The Big Picture at High Energies Fermi Large Area Telescope Map of the entire sky at energies >1 billion times visible light

~100 deg across (thousands of light years)

Glow along the Galactic plane is from cosmic-ray collisions with interstellar gas The giant lobes above and below the Galactic center were entirely unexpected Known as the ‘Fermi Bubbles’ May be evidence of previous intense nuclear activity in the Milky Way 40 Other Gamma-Ray Signals from the Galactic Center: Dark Matter?

On a smaller angular scale Excess Gamma Rays from the Galactic Center region (at energies 100-300 million times visible light) and at lower energies, the central part of the Milky Way is glowing more brightly than expected

One possibility is that this is indirect evidence for particle dark matter ~20 degrees

The energy distribution of Daylan et al. (2016) gamma rays suggests a particle mass of about 30x But… the mass of the proton 41

Gamma-ray excess: Dark Matter or Not?

Pros Cons

The Milky Way (and all galaxies) have The implied annihilation rate is in several times more mass than can be tension with limits from dwarf galaxy accounted for by stars and gas satellites of the Milky Way

The dark matter is so far known only The central Milky Way should from its gravitational effects contain a large, broadly distributed population of millisecond pulsars One plausible theory is that it is so- called WIMPs that do not interact Millisecond pulsars are gamma-ray with light (of course) but can sources annihilate each other At the distance of the Galactic center Gamma rays from the resulting Fermi could not detect them particle cascades would be observed individually, just a glow from their where dark matter is concentrated, overall distribution such as the center of the Milky Way

42 Summary

• Starting ~60 years ago observations outside the visible range opened up the possibility to find and study the Galactic Center • This has been advanced by NASA missions for infrared, X-rays and gamma rays and by ground-based radio and near-infrared observatories • Sgr A* has been found to be a massive black hole powering a (currently) weakly active galaxy • In gamma rays, study of the Galactic center is also motivated by the search for new particle physics, indirect detection of dark matter • This is a very active area of research and requires understanding still more about the center of the Milky Way

• The work described here is within NASA’s Physics of the Cosmos objective in the category of How does the universe work?

TESS Future Studies

JWST 2017-2018

2018

Mid-2020s 44 Additional Resources http://nasawavelength.org/list/1497

Thank you to our presenters!