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Great ObservatoriesGalactic Center Region

Image UnveilingScience Telecon

October 6, 2009

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Multiwavelength Observations

Dr. Frank Summers

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Support Web Site

• http://hubblesource.stsci.edu/events/iyafinale/support/

• Generic press release• Generic media alert

• Composite image caption (PDF)

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Hubble Space Telescope

• Visible, ultraviolet, and infrared observations– 115-2500 nanometers– 2.4 meter mirror

• Launched April 1990• Low Earth orbit

– 600 km– 97 minutes

• Baltimore, MD

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Chandra X-ray Observatory

• X-ray observations– 0.17-17 nanometers– 4 cylindrical mirrors

• Launched July 1999• Elliptical orbit

– 10-140 thousand km– 64 hr 18 min

• Boston, MA

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Spitzer Space Telescope

• Infrared observations– 3-180 microns– 0.85 meter mirror

• Launched August 2003– May 2009 “warm” mission

• Earth-trailing orbit– 0.1 AU per year

• Pasadena, CA

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Chandra

Hubble

Spitzer

Compton

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Galactic Center Region

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90 degrees wide

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12 degrees

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4 degrees

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1 degree

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0.4 degrees

23Hubble – near infrared

24Spitzer – infrared

25Chandra – x-rays

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Spitzer Space Telescope

Dr. Susan Stolovy

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The Galactic Center as Seen From the Spitzer Space Telescope/IRAC

Dr. Susan Stolovy (PI) Spitzer Science Center/Caltech

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The Galactic Center (GC) is invisible at optical wavelengths (0.4-0.7 microns) from Earth even with the largest telescope imaginable! The interstellar dust in the plane of our Milky Way galaxy absorbs the light from the center, which is 26,000 light years away from us. Spitzer’s mid-infrared cameras see through the dust and can cover large areas efficiently.

Artist’s schematic of Milky Way Galaxy (arrow connects the Solar System and the GC) Image courtesy R. Hurt, SSC

Why Observe the Galactic Center with Spitzer?

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The 4 IRAC cameras give us a view extending all the way to the GC: stars (mostly red giants), warm dust, and dark clouds

30The GC is revealed at longer infrared wavelengths!

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Spitzer/IRAC Galactic Center (GC) survey details

Field of View covered: 890 x 640 light years assuming the distance to the GC is 26,000 light years

Area in sky covered is 1.9 x 1.4 degrees (roughly equivalent to area 14 full moons would cover)

Observed with 4 mid-infrared cameras from Infrared Array Camera (IRAC) at 3.6, 4.5, 5.8, and 8.0 microns

3.6 and 4.5 microns show mostly stars and 5.8 and 8.0 show both stars and warm, glowing dust. The glowing dust emission seen in the IRAC images is mostly from tiny, soot-like particles called polycyclic aromatic hydrocarbons (PAH’s). These particles exist on Earth as pollution!

IRAC survey took only 16 hours of telescope time to complete

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8 Micron Image of Galactic Center

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8 Micron image close-ups showing examples of regions where massive stars have recently formed

1 4324 million solar mass black hole hiding here

Quintuplet cluster

34Radio emission is bright at Sgr A* (black hole), supernova remnants, star forming regions, and mysterious linear filaments near strong magnetic fields

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Some Spitzer/IRAC Galactic Center Results

Largest, most sensitive, highest resolution (1-2’’) map of the GC at mid-infrared wavelengths

We see spectacular, complex structure in glowing dust emission, from compact globules to long, stringy filaments

Over one million stars detected in the survey, but region is so crowded that there are many more that we can’t detect

Dark, obscuring clouds seen at many scales Star-forming regions imaged at GC distance and in spiral

arms along the line of sight Follow-up spectroscopy from Spitzer/IRS has led to

discovery of young stellar objects (baby stars) in the GC (An et al. 2009, submitted to ApJL)

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3.6 microns=blue, 4.5 microns=green, 5.8 microns=orange and 8.0 microns=red

Spitzer’s view of the Galactic Center

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Hubble Space Telescope

Dr. Susan Stolovy

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The Galactic Center as Seen from the Hubble Space Telescope/NICMOS

Dr. Susan Stolovy Spitzer Science Center/CaltechPI: D. Wang, UMASS

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The HST survey of ionized hydrogen gas (Paschen alpha) in Galactic Center (GC) was observed using the near-infrared camera on Hubble called NICMOS (Near-Infrared Camera and Multi-Object Spectrometer)

Although there is still much absorption of light at a wavelength of 1.9 microns from the GC by interstellar dust, enough light gets through in deep exposures to make a large-scale map of the ionized gas possible to make.

This is the sharpest image ever of such a large region in the GC; it reveals much about how massive stars form, evolve, and interact with their environment

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HST/NICMOS GC survey details

Field of view covered: 270 x 90 light years assuming the distance to the Galactic Center is 26,000 light years

Area in sky covered is 0.6 x 0.2 degrees, roughly equivalent to area of covered by 1/2 full moon; (it’s cropped to a smaller area in press image, however, about 0.4 degrees across in panel “b”)

The Paschen series of hydrogen spectral lines in the infrared is named after the German physicist Louis Paschen, who discovered them in 1908 (the alpha line, at 1.87 microns, is the strongest of the series). The Earth’s atmosphere absorbs this line from celestial sources, so we need a telescope in space to observe it.

NICMOS observations made in 2 narrow-band filters with wavelengths of 1.87 microns and 1.90 microns. Paschen alpha emission arises from ionized hydrogen gas that excited by hot stars.

Took 144 orbits of telescope time to complete: this is the largest area ever covered by NICMOS by a single program. The data have 10 times better resolution (sharpness) than the Spitzer/IRAC data.

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Making Paschen Alpha images a) F187N filter b) continuum (F190N) subtracted c) stars removed

HST figures from Wang et al., submitted Sept. 2009, MNRAS

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Paschen alpha image

This shows ionized hydrogen emission near sites of massive

stars

1.87 micron image: we detect 600,000 stars!

Note also the dark foreground dust clouds

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a) The central few light years b) the “Pistol”,”Quintuplet” and “Sickle”, c) The Arched filaments: linear features trace local magnetic field

Location of black hole (radio source known as Sgr A*)

“fingers” sculpted by winds from hot stars in Quintuplet cluster

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Close-ups of Selected Nebulae from Pa alpha mosaic of Galactic Center

Several of these are newly discoveredHorizontal bar in each figure shows 0.2 parsecs=0.65 light years

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Some results from the HST data Sharpest view ever of the Galactic Center in a large-scale map;

shows clear signs of interaction of massive stars with environment: “fingers”, bubbles, outflows, etc.

Amazing network of long, straight filaments seen in great detail for first time in ionized gas; some of them follow magnetic field lines;

New compact nebulae discovered with young massive stars, ranging from early to late stages of star formation

Many candidate massive stars identified by bright Pa alpha emission. Some are located OUTSIDE the 3 known clusters in the GC; they may have been thrown out of parent clusters or formed outside clusters

Spectroscopic follow-up shows that many are exotic stars with strong winds. They will explode as supernovae in the future and will have a large impact on future star formation processes in the GC.

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Chandra X-ray Observatory

Dr. Peter Edmonds

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An X-ray view of the Galactic Center

Chandra image

What do the colors mean in this image?

- red: lowest energy X-rays- green: medium energy X-rays- blue: highest energy X-rays

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OVERVIEW

Chandra image is a mixture of: - hot gas, e.g. remnants of supernovas - point sources of different types - star clusters

SOME DETAILS

- Sagittarius A: contains the center of the galaxy and a supermassive black hole - Arches and Quintuplet are star clusters - 1E 1743.1-2843 is a double star

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Sagittarius A*

-- The nearest supermassive black hole to us

-- Weighs about 4 million times the Sun

-- Area close to it is currently surprisingly dim

-- This area was much brighter in the past

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Black holes are “messy eaters”

-- Material around BH heats up and glows

-- Most of the inflowing material swallowed by BH- -- Some is flung outwards along jets/outflows

-- Sgr A* was more like this in the past

Sgr A*’s bigger, more active cousins

MS 0735 Hydra A

close-up (artist’s impression)

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Light echo from Sagittarius A*

-- Area near black hole was about 100,000 - times brighter 50 years earlier

-- Light reflected off clouds 50 yrs later

-- Mass equal to about that of Mercury - was swallowed by the black hole

Artist’s impression of what happened

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More information and graphics at:

http://chandra.harvard.edu/photo/2009/gcenter/http://chandra.harvard.edu/photo/2003/0203long/http://chandra.harvard.edu/photo/2007/gcle/http://chandra.harvard.edu/photo/2009/hydra/http://chandra.harvard.edu/photo/2006/ms0735/

General information about Chandra science and program:

http://chandra.harvard.edu/

Related Chandra products available:Chandra Explores the Milky Way:38x23" Poster, 8 1/2x 11" Litho, 6x8" Postcard, 2x8" Bookmarkhttp://chandra.harvard.edu/edu/request.html

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Final Thoughts

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Further Discussion

• Image Unveiling Google Group– Should have received invitation– Send email to Carolyn to add others– groups.google.com/group/iya-image-unveiling

• Open discussion– Ask questions– Share ideas– Discuss event planning