MASS FUNCTION OF STELLAR REMNANTS IN THE MILKY WAY

Transcription

1 MASS FUNCTION OF STELLAR REMNANTS IN THE MILKY WAY (pron: Woocash Vizhikovsky) Warsaw University Astronomical Observatory Wednesday Seminar, IoA Cambridge, 8 July 2015

2 COLLABORATORS Krzysztof Rybicki (PhD student) Zuzanna Kostrzewa-Rutkowska OGLE team in Warsaw Gaia Alerts team in Cambridge

3 STELLAR REMNANTS Remnants are the products of the final stages of stellar evolution Brown Dwarfs, White Dwarfs, Neutron Stars, Black Holes Problem: most remnants are dark - very hard to find!

4 STELLAR REMNANTS Masses of Neutron Stars (from binaries) - narrow peak around 1.5 MSun (e.g.,kiziltan+2013) Masses of Black Holes (from binaries) - separate peak from ~6 MSun (e.g., Ozel+2010) but no gap between NS and BHs from stellar evolution synthesis and supernovae explosions (e.g., Fryer&Kalogera 2001)

5 MICROLENSING Gravitational lensing by compact lenses (stellar or remnants) Sources: background stars (chance: 10-6 in the Bulge, 10-8 in the LMC) ~1 month astrometry (centroid motion) animations by S.Gaudi photometry (sum of images) ~1mas

6 MICROLENSING About 20% of microlensing events should be due to stellar remnants (Gould 2000) 17% WD 3% NS 0.8% BH 2000 events found every year -> 16 black holes!!! so, why not found yet? Microlensing event rate for different lens populations (Gould 2000) -

7 MICROLENSING mass of the lens from microlensing 1 M = [te (µl µs )] 2 1 DL 1 DS constant Einstein Ring crossing time proper motions lens and source distances lens and source the only parameter measured from a standard microlensing event

8 MICROLENSING to compute the mass of the lens we need both: - Einstein Radius (theta_e) - microlensing parallax (pi_e): high amplification events E M= E astrometry Earth parallax space-based parallax (e.g., Earth-Spitzer)

9 OPTICAL GRAVITATIONAL LENSING EXPERIMENT (OGLE) photo (c) K.Ulaczyk & Ł.Wyrzykowski dedicated 1.3m telescope since 1996 in Las Campanas Obs. Chile

10 OGLE-IV SKY since 2010 Microlensing and Variable Stars Bulge half-billion stars down to 21mag Cadence: red ~30 epochs/night yellow ~10 epochs/night green ~3 epochs/night blue ~1 epoch/night cyan ~1 epoch /2 nights Variables and Transients Magellanic System (LMC+MBR+SMC) 700 sq.deg. limit: 22 mag in I-band cadence: 2-5 nights

11 5 MILLION STARS EVERY 3 MINUTES FoV 1.4 sq.deg., mag limit 21 mag in I-band

12 SEARCH FOR LENSING REMNANTS OGLE-III: millions of stars in the Bulge 3500 standard events (Wyrzykowski+2015) 65 high quality parallax events 25 events with P>50% having a remnant (dark) lens 11 events with P>75% having a remnant (dark) lens 3 BH lens candidates (P>99% remnant) Wyrzykowski+2015

13 BH CANDIDATES OGLE-III event name BLG te [d] Mass [M ] Distance [kpc]

14 BH CANDIDATES OGLE-III event name BLG te [d] Mass [M ] Distance [kpc]

15 BH CANDIDATES the longest microlensing event ever! 7 years of lensing OGLE-III event name BLG te [d] Mass [M ] Distance [kpc]

16 MASS FUNCTION assuming proper motions for sources in the bulge and lenses in the disk individual events mass probability distribution functions P>50% (orange+blue) and P>75% (red+green) of being a dark remnant

17 MASS FUNCTION Finding most probable mass distribution for our samples of remnant events (50% and 75%) broad single gaussian gauss+exp: no gap between NSs and BHs? simulations indicate that we should see the gap in our data if present

18 MICROLENSING to compute the mass of the lens we need both: - Einstein Radius (theta_e) - microlensing parallax (pi_e): high amplification events E M= E astrometry Earth parallax space-based parallax (e.g., Earth-Spitzer)

19 1700deg2 Disk Fields Bulge and Sgr dsph Fields Supernovae Search Fields LMC and SEP Gaia figure by Nadia Blagorodnova, OGLE fields by Jan Skowron OGLE-GAIA SKY

20 MICROLENSING WITH GAIA+OGLE parallax events from 2014 and 2015 also observed by Gaia predicted Gaia astrometric observations for the most probable mass Rybicki+ in prep.

21 MICROLENSING WITH GAIA+OGLE Simulated Gaia astrometry for on-going OGLE parallax events Gaia astrometry expected at <0.1mas level (at the end of the mission) Lens mass recovery at a level of MSun see also Belokurov and Evans (2002)

22 ON-GOING CANDIDATE BH EVENT ogle.astrouw.edu.pl/ogle4/ews/ews.html OGLE event name OGLE-2014-BLG-0613 te [d] Mass [M ] Distance [kpc]

23 SUMMARY there should be dozens of microlensing events due to stellar remnants we found at least 3 strong BH candidates among 65 parallax events found among 150 million stars monitored by OGLE-III total of 11/25 dark remnant lenses mass distribution does not support NS-BH mass gap astrometric data from Gaia combined with OGLE photometry will constrain masses of remnant lenses to 0.1 MSun

24 THANK YOU!

25 TESTING THE ASSUMPTIONS Bulge-Disk and sources at 8kpc Sources at 4kpc instead of 8kpc Bulge-Bulge lensing

26 CANDIDATES Bennett+2001 X-rays - no signal Maeda et al and Nucita et al, 2006