Transcript The Expanding Universe

ASTR1001
Zog: The Second Data Release
Wagner, Bach and Hayden (IAP)
This group have been trying to measure a distance to the blue spots.
They asked for and were awarded time on the Bubble Space Telescope
to look for parallax in the blue spots. No parallax was found: the blue
spots must therefore be more than about fifty light-years away.
Many individual stars in the Greater Milk Stain were also included in their
image of the North Blue Spot. These stars also show no measurable
parallax. They typically have measured fluxes of around 10-16 W m-2 nm-1
in the V band.
Gilbert and Sullivan
This group asked for long exposure images of the blue spots
with the Bubble Space Telescope. The time assignment
committee considered their request to be sensible, as many
astronomers are facinated by these mysterious objects, and
allocated 40 orbits of exposure to each blue spot.
Up close, both blue spots look quite similar to how they appear
unmagnified. Neither breaks up into stars (at the 0.1 arcsecond
resolution of the Bubble Space Telescope), though the North Blue spot
image is full of stars from the Greater Milk Stain.
One surprise: under magnification, the North Blue Spot (the one within
the Greater Milk Stain) has jets of fuzzballs, just like the South Blue
Spot.
Another new result: many new jets of fuzzballs were found around both
blue spots: jets too faint and small to have been seen before. These
faint jets are slightly bluer in colour than the well known bright ones.
Diaz, Heston and Smythe (Ozford Uni)
This team, together with many collaborators, have been
mapping the whole sky, using a special pair of wide field
telescopes.
Such telescopes are called Schmidt telescopes, and use a
special combination of lenses, mirrors and photographic
plates to take photographs of a whopping 36 square degrees
of the sky in one go. Two such telescope, the Palomarz and
Anglo-Auztralian Schmidts, have been photographing the
whole sky for ten years. They have taken these photographs,
digitised them, and have used them to construct a complete
digital map of the sky on 100 cd-roms.
The Anglo-Auztralian Schmidt
The first result concerns the jets. With the all sky digital map
they have been able to show that they extend out from the
North Blue Spot as well as the South one: the northern jets
have, until now, been lost in the midst of the Great Milk Stain.
Furthermore, the Jets seem to extend further out from the
blue spots than anyone previously expected. As they get
further from the spots, the gaps between fuzzballs get very
large, but they can trace some jets out to five degrees from
the blue spots!
The fuzzballs that lie in the jets are always very faint ones:
they never see the famous bright fuzzballs like M23 or M86
in these chains. The jets with bright first members (the
fuzzball furthest from the blue spot) tend to have a bigger
gap between the first and second members. In the table
below they’ve measured the declinations of the first four
members of two jets. The first jet has the brighter first
member.
Galaxy
Order
First
Declination: First Jet
Declination: Second Jet
85.0
-87.0
Second
88.57
-89.40
Third
89.16
-89.67
Forth
89.41
-89.77
They have counted fuzzballs as a function of their
brightness. After calibrating their photographic map, they
came up with a list of over a million fuzzballs: all the
fuzzballs in the sky with fluxes greater than 10-19 W m-2 nm-1,
anywhere in the sky.
The approximate number of fuzzballs as a function of their
flux is listed in the table below.
Total Flux (W m-2 nm-1) as measured Number of Fuzzballs
on Zog.
Flux > 10-15
1
10-15 >Flux > 10-16
28
10-16 >Flux > 10-17
1,150
10-17 >Flux > 10-18
42,000
10-18 >Flux > 10-19
1,550,000
The number of bright fuzzballs (Flux > 10-17 W m-2 nm-1)
per unit area seems to be relatively uniform across the sky
(though they do seem to be concentrations of fuzzballs in a
few places). Fainter fuzzballs, however, are more common
near declination +90 and -90. Near declination zero, the
very faintest fuzzballs are only half as common as they are
at the celestial poles.
Carter and Thoris (Helium Institute)
These researchers managed to persuade the Space
Telescope Science Institute to take a really deep exposure of
a random part of the sky. A really deep exposure takes a lot of
Bubble time, so they were only given time to image one region
of the sky. Furthermore, their data was made generally
available to everyone as soon as it was taken: publicised as
the Bubble Deep Field.
40 orbits of Bubble time were used to image a small region of
the sky at right ascension 0, declination 0, through each of
three filters: B (0.39-0.5 m), V(0.45-0.55 m) and R (0.550.75 m). These were combined to produce a colour image of
this region.
The Bubble Deep Field: 120 orbits exposure with the Wide
Field Planetary Camera 2.
They have counted fuzzballs as a function of their
brightness. They then extrapolated their counts to the
whole sky, assuming that the average density of fuzzballs
in the BDF extends over the whole sky. Their field of view
is too small to measure the space density of brighter
galaxies, and the error bars on the number of galaxies in
the first row is large.
Total Flux (W m-2 nm-1) as measured Number of Fuzzballs
on Zog.
10-16 >Flux > 10-17
800
10-17 >Flux > 10-18
37,000
10-18 >Flux > 10-19
1,200,000
10-19 >Flux > 10-20
51,000,000
10-20 >Flux > 10-21
2,700,000,000
Verdi and Puccini (Venesia Instiute)
Hearing of the recent remarkable discovery of jets around
the North Blue Spot, this group used the William Herzchel
Telescope to get spectra of the fuzzballs in one of these jets.
They obtained spectra of four fuzzballs from one of the
biggest jets extending from the Northern Blue Spot, as
shown below.
B1
B2
B3
B4
Relative Flux
All four fuzzballs had similar spectra: spectra resembling
those of typical stars.
Observed Wavelength (nm)
The only significant differences between the spectra were
that the lines were shifted. All four fuzzballs were
blueshifted - the blueshifts are listed below.
Fuzzball name Blueshift
B1
0.001
B2
0.0043
B3
0.0077
B4
Nearby Stars
0.011
0
Strittmatter and Shu, Zteward Observatory
These two have led a consortium of 73 astronomers from
fifteen countries in doing a massive X-ray and radio survey of
the whole sky.
The radio observations were made with the Auztralia
Telescope Compact Array in the south, and the Very Large
Array in the north. Both groups combined to do an X-ray
survey of the whole sky using the XMM satellite (X-rays do not
penetrate the atmosphere).
The Compact Array
The VLA (Very Large Array)
The X-ray Multi-Mirror (XMM) satellite.
The radio maps
detected thousands of
sources, most of them
looking something like
this. Blue is an optical
image. Red is the radio
map: showing twin jets
extending away from a
small faint fuzzball.
Most sources have
radio fluxes of less than
half a Jansky. The one
spectacular exception is
fuzzball M12, which has
a colossal flux of 11
Janskys.
A Jansky is 10-26 W m-2Hz-1.
Here is an optical image of M12: far and away the most
powerful radio source in the sky. Looks much like a normal
fuzzball. It lies at coordinates RA 236.88, Dec 37.13.
In the radio it looks quite different, as can be seen in these
three images, taken at different resolutions. It seems to
have a jet of relativistic particles squirting out in both
directions.
The second most powerful X-ray and radio source in the
sky was Galaxy NFC64, an optically rather boring fuzzball
that had been observed with the BST by Group 1 in the
first round of observations. XMM detected 27 X-rays per
second from it.
It was also a double radio source, though the two jets were
of more similar brightness than those of M12.
The two blue spots were not strong X-ray or radio sources.
However, all the fuzzballs in one jet sticking out of the
Southern Blue Spot were strong X-ray and radio sources.
The same applies to the Northern blue spot: all the fuzzballs
in one jet sticking out of it were strong X-ray and radio
sources.
The Radio and X-ray Jet
The other jets radiating from the blue spots did not emit strong
radio or X-ray flux. No new jets were discovered, travelling in
any direction. Published images were checked, and this jet
seems similar to all the others optically. In the radio, all
sources in both chains are double radio sources, similar to
M12 and NFC64. All the radio axes point in the same way
(roughly perpendicular to the direction of the jets).
Name
A
B
C
D
E
Right
Ascension
236.88
236.88
236.88
236.88
236.88
Declination X-rays per
second
-81.26
5.5
-84.42
2.2
-85.90
1.2
-86.76
0.8
-87.33
0.5
Details of the Southern Radio/X-ray Jet
Here are the details of the Northern Jet. As with the Southern
Jet, the brightest source, which in both cases is the furthest
from the Blue Spot, is called ‘A’, and the others are numbered
in order as they approach the blue spots. There are many
more members of both jets - only those from which more than
0.5 X-rays per second are detected are listed.
Name
A
B
C
D
E
Right
Ascension
236.88
236.88
236.88
236.88
236.88
Declination X-rays per
second
+78.0
10.2
+83.2
3.3
+85.3
1.6
+86.4
0.9
+87.1
0.6
Details of the Northern Radio/X-ray Jet
De Canis et al.
This group have been slowly and painstakingly searching for
variable stars in the central regions of the Greater Milk Stain.
This is very difficult work as these stars are faint - the power
of the Very Large Telescope (VLT), with its four 8m mirrors
was required.
Stars pulsing with 2 hour periods were found.
They further seached for such pulsing stars in two of the
brightest fuzzballs in the sky: M23 and M86. This
observation required the Bubble Space Telescope. Once
again, they were successful in finding stars with 2 hour
pulsation periods.
The Very Large Telescope
Here is a table of the average peak brightness of the 2-hour
pulsing stars in the three targets.
Target
GMS
Average Peak V-band
Flux (Wm-2nm-1)
1.0x10-16
M23
2.1x10-22
M86
7.3x10-23
Smoot and Hawkins
These reseaarchers built a satellite to measure the
microwave background radiation.
Using ground-based microwave telescopes, it was quickly
established that a microwave background does indeed exist.
Their Cosmic Background Explorer satellite was launched to
measure this background precisely.
The microwave background was rapidly discovered to vary in
brightness across the sky. It is about 10% brighter in the
direction of both blue spots than it is at Declination zero.
Here is an all-sky map of the microwave background.
Declination zero is along the middle. Declination +90 is at
the top and -90 is at the bottom. The intensity at
declination +90 or -90 is 10% greater than that at
Declination 0.
When this simple correlation with declination is removed from the data, some
residual lumps are seen. These residual brightness patterns have an
amplitude of about 0.001% (ie. the brightest bits are 0.001% brighter than the
faintest bits).
Remarkably, the pattern of bright and dark regions looking towards
Declination +90 and -90 are the same! The same structures are seen!
The structures do not seem to correlate with fuzzballs or the milkstains.
0 RA
0 RA
90 RA
90 RA
+90 Dec:
North
-90 Dec:
South
Fidelis and Semper
This group requested BST spectra of the objects found in the
Bubble Deep Field, in particular the blue galaxy-like objects,
the small red objects, and the objects that look like fuzzy balls.
The time allocation committee rejected this proposal: given
that it took 120 orbits to even get an image of these things,
obtaining spectra would require about 10,000 orbits - four
years of exclusive BST time. The committee were not
convinced that useful science would come out of this colossal
investment of time.
The group did, however, persuade some collaborators with
access to the Keck Telescope, Zog’s biggest ground-based
telescope, to get spectra of a few of the brightest sources in
the Bubble Deep Field. The small red objects were far too faint
to obtain spectra, but a few ratty spectra were obtained of the
brightest blue elongated things and the grey fuzzy balls.
The Bubble Deep Field: 120 orbits exposure with the Wide
Field Planetary Camera 2.
The Keck Telescope
Relative Flux
The blue, elongated things had featureless, blue spectra. No emission or
absorption-lines were seen, but the signal-to-noise ratio of the spectra was so
poor that this wasn’t really a surprise (these are very difficult things to get
spectra of).
300nm
Observed Wavelength (nm)
700nm
Relative Flux
The faint fuzzy things had rather different spectra, though still pretty
ratty. Here is a typical one.
300
600
900
Observed Wavelength (nm)
Walrus et al.
Walrus et al are experimental physicists. Hearing all the talk
about strange geometries, they requested money to build an
instrument to measure p.
Two instruments were built: one to measure it in the lab, and
one to measure it on much larger scales in space (by bouncing
lasers between spacecraft).
The ground-based experiment reported that p had its normal,
expected value with a precision of 15 decimal places.
The space-based experiment measured p on a scale of 1012m,
and once again found that it has its normal expected value, to
an accuracy this time of 10 decimal places.
Gabriel, Nunn and Weekes (ANU)
Gabriel et al. requested an X-ray measurement of the famous
radio source M12.
The observations were made, and a very strong emission was
detected: 149 X-rays per second.
The European Zpace Agency (EZA)
EZA have long been concerned that not enough is
known about nearby stars. The fundamental problem
has always been measuring the distances to stars:
unless you know the distance, everything else is very
hard to determine. They recently launched the
Hipparchoz satellite, designed to measure parallax with
unprecedented precision to all stars within about 30 pc.
When its two year mission was completed, it took the
team scientists another two years to process the vast
amounts of data.
Hipparchoz
Parallax Measurements
Despite the enormous increase in precision, no parallax
was measured for either blue spot. Likewise, no fuzzball
showed parallax, and none of the stars in the GMS showed
measurable parallax.
Over 7,000 nearby stars did, however, show parallax. Of
particular interest were 4 pulsing stars with two hour
periods. These stars were chosen because their spectra
were very similar to the two-hour pulsing stars seen in the
GMS and in other fuzzballs.
Parallaxes are measured in arcseconds (and arcsecond is
1/60 arcminutes. An arc-minute is 1/60 degrees). They
represent the change in apparent position over half a Zog
year (ie. The coordinates of the star change by this angle
between two observations six months apart).
Variable Star Data
Star Name
HD666123
Parallax (Arcsec) Measured Flux
(W m-2 nm-1)
0.09
1.066x10-13
HD546121
0.334
1.589x10-12
HD273364
0.167
3.969x10-13
HD987123
0.11
1.607x10-13
Radar Measurements
Radar pulses sent to Zog’s sun take 18 minutes 53.33
seconds to make the round trip to the sun and back.
The speed of light, as measured in Zoggian laboratories, is
the same as it is on Earth.