Reconnection in Space

Andris Vaivads

Uppsala, 2004-06-07

Uppsala University, Department of Astronomy and Space Physics, Institute of Space Physics

... include parts that my 1 year old daughter could understand

... include parts that nobody understands

Docent lecture

after lecture - cake refreshments at 3rd floor

research

Energy

Magnetic field

Reconnection concept

Reconnection examples

Reconnection research

Reconnection in space

For those who want some proof that physicists are human, the proof is in the idiocy of all the different units which they use for measuring energy.

The Character of Physical Law (1967) R.P. Feynman.

Energy

J, °C, °F, K, degrees, eV, erg, cal, ...

Measuring energy

1eV

10eV

+

-

+

-

hn

atoms

ions

electrons

photons

1 eV – infrared

2 eV - visible light

4 eV – ultraviolet

1keV – X rays

1MeV – gamma rays

Sun

Surface temperature ~6000 °C

2 eV

1keV

4 eV

l [mm]

hn[eV]

2

1

4

8

Highest energies in space above the Sun!

Trace, 2eV, 7eV

Energy should come from somewhere!

Sunny day

on Earth

°C	eV

on Sun	6000	0.5

space around Sun	106	100

on Earth	30	0.026

space around Earth	103-108	0.1-10000

center of Sun	15 106	1300

Particle energies

Ionization

Energy necessary to create an ion and electron from one atom

+

-

+

-

5-20 eV

Highest energies in space above the Sun!

Energy should come from somewhere!

Space is ionized – plasma!

Hubble Ultra Deep Field ,

Where are the highest energies in universe?

Credit: NASA/CXC/STScI/U.North Carolina/G.Cecil

NGC 3079

Chandra X ray

Hubble optical

Paris

sunny working day

Magnetic field

Think in magnetic field lines! .. without ends!

Magnetic flux tube energy W

Magnetic

field lines

Magnetic pressure

Magnetic tension

W > W

Magnetic energy converted into kinetic energy of ions and electrons

Magnetic

flux tubes

In space there are many places with much more energy in magnetic field than in ions and electrons. Source of high energy particles?!

Reconnection – the idea

A narrow current sheet separates in space regions of different plasmas and oppositely directed magnetic field

Reconnection – topology changes allowing interconnection of magnetic field lines from both regions.
Two ways 1) EII≠0, 2) B=0.

flows

reconnection jets

Reconnection – energy conversion as a result of reconnection

Numerical simulation

Reconnection – the point

flows

reconnection jets

Numerical simulation

Topology – allows energy and mass transport across boundary

Energy – the magnetic field energy is built up by many particles but is converted to the kinetic energy of few which therefore receive high energies.

topology vs. energy

Examples from space

Galactic halo

Proton aurora

Sun

Galaxies

Earth

Solar flare

Solar wind and Earth magnetosphere

Solar wind and Earth magnetosphere

Topology

Energy

Magnetotail

energy storage (B)

Magnetopause

energy transfer

Topology

Tsyganenko model

Solar flares

Xflare movie

Astrophysical jets

On a way to understand reconnection

Theory
- do the right approximations
- give up and turn to numerical simulations

Numerical simulations
- take the right equations (MHD, HMHD, particles)
- put into the code and study results

Experiment
- space in situ / astro / laboratory
- most detailed observations from space in situ!

Reconnection – topics

flows

reconnection jets

Numerical simulation

Structure

Continuity

Remote sensing

Reconnection rate

Guide field

Relative importance

Acceleration mechanisms (E)

X-line

[Rogers]

Numerical simulations

[Birn et al., 2001]

Reconnected flux

GEM challange

Hall term important!

- whistlers

- Kinetic Alfvén waves

[Rogers]

out of plane magnetic field

- quadrupolar structure

Numerical simulations

[Hoshino et al., 2001]

Separatrices

- strong electric fields

- strong parallel currents

- electron beams

Reconnection & space physics

[Phan et al., 2000]

Reconnection jets

Continuity

Reconnection & space physics

Why space in situ : we can measure local magnetic and electric fields, as well as ion and electron distribution functions.

[Mozer et al., 2002]

[Retino et al., 2004]

Cluster chasing X-line

4 s/c ESA “Cornerstone”

2000-2005

First time we can reliably solve
time-space ambiguity

First time reliable measurements of
current

2D

c/pi~100km

c/pe~2km

Current

[Rogers et al., 2000]

Cluster, separatrices far from X-line

Narrow strong current sheet

e- beams

Hall dynamics

[André et al., 2004]

Cluster, close to X-line

Reliable structure estimate

Hall dynamics

Fast reconnection

[Vaivads et al., 2004]

Separatrices, jII and HF waves

[Vaivads et al., 2004]

Strong parallel currents

Langmuir/upper hybrid emissions

The role of waves?
(anomalous resistivity, diffusion)

[Khotyaintsev et al., 2004]

Reconnection summary:

Magnetic field topology changes and energy conversion

Reconnection jets, plasma energization

PLASMA (low energy) > B > plasma (HIGH ENERGY)

In space around planets, stars, black holes, ...

We start to understand details

Chandra Deep Field

This composite image was assembled from exposures taken by the near-infrared camera and the advanced camera. Astronomers incorporated the advanced camera's visible-light observations into the image to better discriminate the colors of the distant galaxies. The near-infrared camera observations were taken from Sept. 3 to Nov. 27, 2003.

Astronomers at the Space Telescope Science Institute today unveiled the deepest portrait of the visible universe ever achieved by humankind. Called the Hubble Ultra Deep Field (HUDF), the million-second-long exposure reveals the first galaxies to emerge from the so-called "dark ages," the time shortly after the big bang when the first stars reheated the cold, dark universe. The new image should offer new insights into what types of objects reheated the universe long ago.

This historic new view is actually two separate images taken by Hubble's Advanced Camera for Surveys (ACS) and the Near Infrared Camera and Multi-object Spectrometer (NICMOS). Both images reveal galaxies that are too faint to be seen by ground-based telescopes, or even in Hubble's previous faraway looks, called the Hubble Deep Fields (HDFs), taken in 1995 and 1998.

"Hubble takes us to within a stone's throw of the big bang itself," says Massimo Stiavelli of the Space Telescope Science Institute in Baltimore, Md., and the HUDF project lead. The combination of ACS and NICMOS images will be used to search for galaxies that existed between 400 and 800 million years (corresponding to a redshift range of 7 to 12) after the big bang. A key question for HUDF astronomers is whether the universe appears to be the same at this very early time as it did when the cosmos was between 1 and 2 billion years old.

The HUDF field contains an estimated 10,000 galaxies. In ground-based images, the patch of sky in which the galaxies reside (just one-tenth the diameter of the full Moon) is largely empty. Located in the constellation Fornax, the region is below the constellation Orion.

The final ACS image, assembled by Anton Koekemoer of the Space Telescope Science Institute, is studded with a wide range of galaxies of various sizes, shapes, and colors. In vibrant contrast to the image's rich harvest of classic spiral and elliptical galaxies, there is a zoo of oddball galaxies littering the field. Some look like toothpicks; others like links on a bracelet. A few appear to be interacting. Their strange shapes are a far cry from the majestic spiral and elliptical galaxies we see today. These oddball galaxies chronicle a period when the universe was more chaotic. Order and structure were just beginning to emerge.

Installed in 2002 during the last servicing mission to the Hubble telescope, the ACS has twice the field of view and a higher sensitivity than the older workhorse camera, the Wide Field Planetary Camera 2, installed during the 1993 servicing mission. "The large discovery efficiency of the ACS is now being exploited in sky surveys such as the HUDF," Stiavelli says.

The NICMOS sees even farther than the ACS. The NICMOS reveals the farthest galaxies ever seen, because the expanding universe has stretched their light into the near-infrared portion of the spectrum. "The NICMOS provides important additional scientific content to cosmological studies in the HUDF," says Rodger Thompson of the University of Arizona and the NICMOS Principal Investigator. The ACS uncovered galaxies that existed 800 million years after the big bang (at a redshift of 7). But the NICMOS may have spotted galaxies that lived just 400 million years after the birth of the cosmos (at a redshift of 12). Thompson must confirm the NICMOS discovery with follow-up research.

"The images will also help us prepare for the next step from NICMOS on the Hubble telescope to the James Webb Space Telescope (JWST)," Thompson explains. "The NICMOS images reach back to the distance and time that JWST is destined to explore at much greater sensitivity." In addition to distant galaxies, the longer infrared wavelengths are sensitive to galaxies that are intrinsically red, such as elliptical galaxies and galaxies that have red colors due to a high degree of dust absorption.

The entire HUDF also was observed with the advanced camera's "grism" spectrograph, a hybrid prism and diffraction grating. "The grism spectra have already yielded the identification of about a thousand objects. Included among them are some of the intensely faint and red points of light in the ACS image, prime candidates for distant galaxies," says Sangeeta Malhotra of the Space Telescope Science Institute and the Principal Investigator for the Ultra Deep Field's ACS grism follow-up study. "Based on those identifications, some of these objects are among the farthest and youngest galaxies ever seen. The grism spectra also distinguish among other types of very red objects, such as old and dusty red galaxies, quasars, and cool dwarf stars."

Galaxies evolved so quickly in the universe that their most important changes happened within a billion years of the big bang. "Where the HDFs showed galaxies when they were youngsters, the HUDF reveals them as toddlers, enmeshed in a period of rapid developmental changes," Stiavelli says.

Hubble's ACS allows astronomers to see galaxies two to four times fainter than Hubble could view previously, and is also very sensitive to the near-infrared radiation that allows astronomers to pluck out some of the farthest observable galaxies in the universe. This will hold the record as the deepest-ever view of the universe until ESA, together with NASA, launches the James Webb Space Telescope in 2011.

Though ground-based telescopes have, to date, spied objects that existed just 500 million years after the big bang (at a redshift of 10), they need the help of a rare natural zoom lens in space, called a gravitational lens, to see them. However, the ACS can reveal typical galaxies at these great distances. Even much larger ground-based telescopes with adaptive optics cannot reproduce such a view. The ACS picture required a series of exposures taken over the course of 400 Hubble orbits around Earth. This is such a big chunk of the telescope's annual observing time that Institute Director Steven Beckwith used his own Director's Discretionary Time to provide the needed resources.

The HUDF observations began Sept. 24, 2003 and continued through Jan. 16, 2004. The telescope's ACS camera, the size of a phone booth, captured ancient photons of light that began traversing the universe even before Earth existed. Photons of light from the very faintest objects arrived at a trickle of one photon per minute, compared with millions of photons per minute from nearer galaxies.

Just like the previous HDFs, the new data are expected to galvanize the astronomical community and lead to dozens of research papers that will offer new insights into the birth and evolution of galaxies.

Release Date: 9:30AM (EST) March 9, 2004

Release Number: STScI-2004-07

Contact:

Don Savage

NASA Headquarters, Washington

(Phone: 202-358-1547; E-mail: donald.l.savage@nasa.gov)

Ray Villard

Space Telescope Science Institute, Baltimore, MD

(Phone: 410-338-4514; E-mail: villard@stsci.edu)

Lars Lindberg Christensen

Hubble European Space Agency Information Centre

(Phone: 011-49-89-320-06-306; Cell: 011-49-173-38-72-621;

E-mail: lars@eso.org)

Lori Stiles

University of Arizona News Service, Tucson

(Phone: 520-626-4402; E-mail: lstiles@u.arizona.edu)

Solar spectrum from http://sd.znet.com/~schester/facts/solar_energy.html

Andris Vaivads

2004-03-02T22:08:50