ASTR1001

Zog: The Second Data Release

Results to dateIn a recent article in Scientific Zoggian, Prof Paul Franciz suggests that the astronomical community seems to have reached a consensus on some issues.

Virtually everyone seems to agree that the Greater Milkstain is a collection of around 10 million stars, clustered in the centre. Our own star seems to lie in the outer regions of this vast star cluster, which we are calling a “galaxy”.

It is also widely (but not universally) accepted that at least some fuzzballs are other “galaxies” much like our own.

There have been a few attempts to estimate the size of the GMS, and distances to other fuzzballs, but there is no consensus yet on these values.

Fuzzballs show both red- and blue shifts. No clear pattern has yet emerged, and the blue spots remain an enigma.

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.

GalaxyOrder

Declination: First Jet Declination: Second Jet

First 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 measuredon Zog.

Number of Fuzzballs

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 (0.55-0.75 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 measuredon Zog.

Number of Fuzzballs

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

B2B3

B4

All four fuzzballs had similar spectra: spectra resembling those of typical stars.

Observed Wavelength (nm)

Rel

ativ

e F

lux

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 BlueshiftB1 0.001

B2 0.0043

B3 0.0077

B4 0.011

Nearby Stars 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 RightAscension

Declination X-rays persecond

A 236.88 -81.26 5.5B 236.88 -84.42 2.2

C 236.88 -85.90 1.2

D 236.88 -86.76 0.8E 236.88 -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 RightAscension

Declination X-rays persecond

A 236.88 +78.0 10.2B 236.88 +83.2 3.3

C 236.88 +85.3 1.6

D 236.88 +86.4 0.9E 236.88 +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 Average Peak V-bandFlux (Wm-2nm-1)

GMS 1.0x10-16

M23 2.1x10-22

M86 7.3x10-23